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Science M.C.Q. [1 M]

Atoms and Molecules · Gujarat Board (GSEB) STD 9 (GSEB - English Medium). 40 questions.

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M.C.Q. [1 M]

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Question 11 Mark
If 1.4g of calcium oxide is formed by the complete decomposition of calcium carbonate, then the amount of calcium carbonate taken and the amount of carbon dioxide formed will be respectively:
  1. 2.2g and 1.1g
  2. 1.1g and 2.5g
  3. 2.5g and 1.1g
  4. 5.0g and 1.1g
Answer
  1. 2.5g and 1.1g

Explanation:

Molecular mass of CaCO3: 40 + 12 + (16 × 3) = 100g

Molecular mass of CaO: 40 + 16 = 56g

Molecular mass of CO2: 12 + (16 × 2) = 44g

Reaction for the decomposition of calcium carbonate:

$\text{CaCO}_3\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ }\text{CaO}\ +\ \text{CO}_2\\ \ \ 100\text{g} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 56\text{g}\ \ \ \ \ \ \ \ 44\text{g}\\\ \ \ \ \text{X}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 1.4\text{g}\ \ \ \ \ \ \ \ \ \text{Y}$

56g of CaO is obtained when 100g of CaCO3 is burnt.

Therefore, to get 1.4g of CaO, the amount of CaCO3 to be burnt will be $\frac{100\ \times\ 1.4}{56}=2.5\text{g}$

For CO2,

100g of CaCO3 yields 44g of CO2

Therefore, 2.5g of CaCO3 will yield $\frac{44\ \times\ 2.5}{100}=1.1\text{g}$

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Question 21 Mark
The atomic number of an element E is 16. The number of electrons in ion E2- will be:
  1. 16
  2. 18
  3. 15
  4. 14
Answer
  1. 18

Explanation:

Element with an atomic number 16 will have 18 electrons in its E2- ion because anions are formed by gaining electrons.

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Question 31 Mark
The anion of an element has:
  1. More electrons than the normal atom.
  2. Less electrons than the normal atom.
  3. More protons than the normal atom.
  4. Same number of electrons as normal atom.
Answer
  1. More electrons than the normal atom.

Explanation:

The anion of an element has more electrons than the normal atom because it is formed by gaining electrons.

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Question 41 Mark
The Latin language name of an element is natrium. The English name of this element is:
  1. Sodium.
  2. Potassium.
  3. Magnesium.
  4. Sulphur.
Answer
  1. Sodium.

Explanation:

The English name of the element natrium is Sodium(Na).

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Question 51 Mark
The atoms of which of the following pair of elements are most likely to exist in free state?
  1. Hydrogen and helium.
  2. Argon and carbon.
  3. Neon and nitrogen.
  4. Helium and neon.
Answer
  1. Helium and neon.

Explanation:

Atoms of helium and neon exist in a free state because they are inert gases and chemically inactive.

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Question 61 Mark
In hydrogen peroxide (H2O2), the proportion of hydrogen and oxygen by mass is:
  1. 1 : 8
  2. 1 : 16
  3. 8 : 1
  4. 16 : 1
Answer
  1. 1 : 16

Explanation:

In hydrogen peroxide, the ratio of hydrogen to oxygen is 1 : 16 by mass.

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Question 71 Mark
If 32g of sulphur has x atoms, then the number of atoms in 32g of oxygen will be:
  1. $\frac{\text{x}}{2}$
  2. 2x
  3. x
  4. 4x
Answer
  1. 2x

Explanation:

The number of oxygen atoms in 32g of oxygen will be 2x.

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Question 81 Mark
If the number of electrons in an ion Z3- is 10, the atomic number of element Z will be:
  1. 7
  2. 5
  3. 10
  4. 8
Answer
  1. 7

Explanation:

If the number of electrons in an ion Z3- is 10, the atomic number of element Z will be 7 because the ion is formed by gaining three electrons.

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Question 91 Mark
The law of conservation of mass was given by:
  1. Dalton.
  2. Proust.
  3. Lavoisier.
  4. Berzelius.
Answer
  1. Lavoisier.

Explanation:

The law of conservation of mass was given by Lavoisier.

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Question 101 Mark
Which of the following correctly represents 360g water?
  1. 2 moles of H2O.
  2. 20 moles 0f water.
  3. 6.022 × 1023 molecules of water.
  4. 1.2044 × 1025 molecules of water.
  1. (i)
  2. (i) and (iv)
  3. (ii) and (iii)
  4. (ii) and (iv)
Answer
  1. (ii) and (iv)

Explanation:

20 moles of water and 1.2044 × 1025 molecules of water correctly represent 360gms of water.

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Question 111 Mark
A particle X has 17 protons, 18 neutrons and 18 electrons. This particle is most likely to be:
  1. A cation.
  2. An anion.
  3. A molecule.
  4. A compound.
Answer
  1. An anion.

Explanation:

X, most likely, is an anion because the number of electrons is more than the number of protons.

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Question 121 Mark
Molecular compounds are usually formed by the combination between:
  1. A metal and a non-metal.
  2. Two different non-metals.
  3. Two different metals.
  4. Any two gaseous elements.
Answer
  1. Two different non-metals.

Explanation:

Molecular compounds are formed by the combination of two different non-metals.

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Question 131 Mark
The ratio of moles of atoms in 12g of magnesium and 16g of sulphur will be:
  1. 3 : 4
  2. 4 : 3
  3. 1 : 1
  4. 1 : 2
Answer
  1. 1 : 1

Explanation:

The ratio of moles of atoms in 12g of Magnesium and 16g of Sulphur will be 1 : 1

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Question 141 Mark
A particle P has 18 electrons, 20 neutrons and 19 protons. This particle must be:
  1. A molecule.
  2. A binary compound.
  3. An anion.
  4. A cation.
Answer
  1. A cation.

Explanation:

Particle P must be a cation.

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Question 151 Mark
The formula of a compound is X3Y. The valencies of elements X and Y will be respectively:
  1. 1 and 3
  2. 3 and 1
  3. 2 and 3
  4. 3 and 2
Answer
  1. 1 and 3

Explanation:

Valencies of element X and Y will be 1 and 3, respectively.

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Question 161 Mark
The symbols of the elements cobalt, aluminium, helium and sodium respectively written by a student are as follows. Which symbol is the correct one?
  1. CO
  2. AL
  3. He
  4. So
Answer
  1. He

Explanation:

The correct symbols of cobalt, aluminium, and sodium are Co, Al and Na respectively.

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Question 171 Mark
One of the following elements has an atomicity of ‘one’. This element is:
  1. Helium.
  2. Hydrogen.
  3. Sulphur.
  4. Ozone.
Answer
  1. Helium.

Explanation:

The atomicity of Helium(He) is 1.

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Question 181 Mark
A student wants to have 3.011 × 1023 atoms each of magnesium and carbon elements. For this purpose, he will have to weigh:
  1. 24g of magnesium and 6g of carbon.
  2. 12g of carbon and 24g of magnesium.
  3. 20g of magnesium and 10g of carbon.
  4. 12g of magnesium and 6g of carbon.
Answer
  1. 12g of magnesium and 6g of carbon.

Explanation:

The student will have to weigh 12g of Magnesium and 6g of Carbon.

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Question 191 Mark
Two elements X and Y have valencies of 5 and 3, and 3 and 2, respectively. The elements X and Y are most likely to be respectively:
  1. Copper and sulphur.
  2. Sulphur and iron.
  3. Phosphorus and nitrogen.
  4. Nitrogen and iron.
Answer
  1. Nitrogen and iron.

Explanation:

Elements X and Y, most likely, are nitrogen and iron.

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Question 201 Mark
In water, the proportion of oxygen and hydrogen by mass is:
  1. 1 : 4
  2. 1 : 8
  3. 4 : 1
  4. 8 : 1
Answer
  1. 8 : 1

Explanation:

In water, the ratio of oxygen to hydrogen is 8 : 1 by mass.

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Question 211 Mark
Which of the following represents a correct chemical formula?
  1. CaCl
  2. Na3N
  3. NaSO4
  4. NaS
Answer
  1. Na3N

Explanation:

The correct chemical formula among the listed chemicals is of Na3N.

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Question 221 Mark
The number of electrons in an ion Y2+ is 10. The atomic number of element Y is most likely to be:
  1. 8
  2. 12
  3. 10
  4. 14
Answer
  1. 12

Explanation:

The atomic number of element Y would be 12.

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Question 231 Mark
The law of constant phosphorus, sulphur and krypton, the elements having the lowest and highest atomicities are respectively:
  1. Sulphur and krypton.
  2. Krypton and ozone.
  3. Phosphorus and sulphur.
  4. Krypton and sulphur.
Answer
  1. Krypton and sulphur.

Explanation:

Out of ozone, phosphorus, sulphur and krypton, krypton has the lowest atomicity and sulphur the highest .

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Question 241 Mark
An ionic compound will be formed by the combination of one of the following pairs of elements. This pair of elements is:
  1. Chlorine and calcium.
  2. Calcium and sodium.
  3. Sulphur and carbon.
  4. Chlorine and chlorine.
Answer
  1. Chlorine and calcium.

Explanation:

Chlorine and calcium can form an ionic compound CaCl2.

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Question 251 Mark
The scientist who proposed the first letter (or first letter and another letter) of the Latin or English name of an element as its symbol, was:
  1. Dalton.
  2. Proust.
  3. Lavoisier.
  4. Berzelius.
Answer
  1. Berzelius.

Explanation:

Berzelius proposed the first letter (or first letter and another letter) of the Latin or English name of any element as its symbol.

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Question 261 Mark
The English name of an element is potassium, its Latin name will be:
  1. Plumbum.
  2. Cuprum.
  3. Kalium.
  4. Natrium.
Answer
  1. Kalium.

Explanation:

The Latin name of the element potassium is kalium. Hence, the symbol for potassium is K.

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Question 271 Mark
The atomic number of an element X is 13. What will be the number of electrons in its ion X3+?
  1. 11
  2. 15
  3. 16
  4. 10
Answer
  1. 10

Explanation:

If the atomic number of X is 13, the number of electrons in its X3+ ion would be 13 - 3 = 10.

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Question 281 Mark
Which of the following pair of elements represents a mole ratio of 1 : 1?
  1. 10g of calcium and 12g of magnesium.
  2. 12g of magnesium and 6g of carbon.
  3. 12g of carbon and 20g of calcium.
  4. 20g of sodium and 20g of calcium.
Answer
  1. 12g of magnesium and 6g of carbon.

Explanation:

12g of magnesium and 6g of carbon will have a mole ratio of 1 : 1

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Question 291 Mark
The atomic theory of matter was proposed by:
  1. John Kennedy.
  2. Lavoisier.
  3. Proust.
  4. John Dalton.
Answer
  1. John Dalton.

Explanation:

The atomic theory of matter was proposed by John Dalton.

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Question 301 Mark
The formula of the sulphate of an element X is X2(SO4)3. The formula of nitride of element X will be:
  1. X2N
  2. XN2
  3. XN
  4. X2N3
Answer
  1. XN

Explanation:

Formula of nitride of the element X will be XN.

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Question 311 Mark
Which of the following has the maximum number of atoms?
  1. 18g of H2O
  2. 18g of O2
  3. 18g of CO2
  4. 18g of CH4
Answer
  1. 18g of CH4

Explanation:

18g of CH4 has  maximum number of atoms.

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Question 321 Mark
The law of constant proportions was given by:
  1. Proust.
  2. Lavoisier.
  3. Dalton.
  4. Berzelius.
Answer
  1. Proust.

Explanation:

The law of constant proportion was proposed by Joseph Proust.

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Question 331 Mark
If 12 gram of carbon has x atoms, then the number of atoms in 12 grams of magnesium will be:
  1. x
  2. 2x
  3. $\frac{\text{x}}{2}$
  4. 1.5x
Answer
  1. $\frac{\text{x}}{2}$

Explanation:

The number of atoms in 12g of magnesium will be $\frac{\text{x}}{2}$

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Question 341 Mark
One nm is equal to:
  1. 10-9mm.
  2. 10-7cm.
  3. 10-9cm.
  4. 10-6m.
Answer
  1. 10-7cm.

Explanation:

One nanometre is equal to 10-7 centimetre.

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Question 351 Mark
An element which can exhibit valencies of 2, 4 and 6 can be:
  1. Copper.
  2. Iron.
  3. Mercury.
  4. Sulphur.
Answer
  1. Sulphur.

Explanation:

Sulphur exhibits the valencies of 2, 4 and 6.

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Question 361 Mark
The symbol of a metal element which is used in making thermometers is:
  1. Ag
  2. Hg
  3. Mg
  4. Sg
Answer
  1. Hg

Explanation:

The symbol of the metal used in making thermometers is Hg(Mercury).

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Question 371 Mark
The atomicities of ozone, sulphur, phosphorus and argon are respectively:
  1. 8, 3, 4 and 1
  2. 1, 3, 4 and 8
  3. 4, 1, 8 and 3
  4. 3, 8, 4 and 1
Answer
  1. 3, 8, 4 and 1

Explanation:

The atomicity of ozone(O3) is 3, sulphur(S)- 8, phosphorus(P)- 4, Argon(noble gas, Ar)- 1.

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Question 381 Mark
The element having atomicity ‘four’ is most likely to be:
  1. Argon.
  2. Fluorine.
  3. Phosphorus.
  4. Francium.
Answer
  1. Phosphorus.

Explanation:

Phosphorus has an atomicity of 4.

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Question 391 Mark
Which of the following elements has the same molecular mass as its atomic mass?
  1. Nitrogen.
  2. Neon.
  3. Oxygen.
  4. Chlorine.
Answer
  1. Neon.

Explanation:

Neon’s molecular mass is equivalent to its atomic mass.

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Question 401 Mark
The cation of an element has:
  1. The same number of electrons as its neutral atom.
  2. More electrons than a neutral atom.
  3. Less protons than a neutral atom.
  4. Less electrons than a neutral atom.
Answer
  1. Less electrons than a neutral atom.

Explanation:

The cation of an element has less electrons than a neutral atom.

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