Science M.C.Q. [1 M]

The first model of an atom was given by $J.J.$ Thomson. According to him, an atom consists of a sphere of positive charge with negatively charged electrons embedded in it.

Chloride ion, $\mathrm{Cl}^{-}$has $18$ electrons so, its electronic configuration is $2, 8, 8.$

Atomic number = Number of protons $= 3$
Mass number = Number of protons $+$ number of neutrons $=3 + 4 = 7$
Electronic configuration of the atom is $2, 1(K,L)$
Hence, its valency is $1.$

Mass number of the element $=27$
Number of neutrons $=14$
Number of protons $=$ mass number - number of neutrons
$= 27 - 14 = 13$
As the ion of this element has $3$ positive charges, it means that it has lost $3$ electrons. Therefore, there are now $10$ electrons in the ion.

The valency of Ne is zero as it is a noble gas and thus does not take part in bond formation.
Cl has electronic configuration: $2, 8, 7.$
Therefore, Cl will accept one electron to attain stable noble gas configuration.
Thus valency of $Cl$ is $1.$

Carbon has $4$ electrons in its outermost orbit. It completes its octet by sharing $4$ electrons.

Graphite is an allotrope of carbon. It is made up of all $C$ atoms. The atomic number of carbon is $6$; so, the number of valence electrons is $4.$

The atomic number of oxygen is $8.$
The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus. Also, atomic number is the number of protons present in the nucleus.
Since the number of neutrons present in oxygen is $8$ and the given mass is $16.$
Therefore, the number of neutrons will be equal to $8$ i.e. $16−8.$

Given, Atomic number$= 13$
We know that, $Z=$ Atomic Number= Number of protons.
Therefore, number of proton$=13$
We know that Mass no. of an atom $=$ No. of protons + No. of neutrons.
Mass no $=$ atomic mass $=27 u$
$27 u=13+n \text { Or, } n=27-13=14$
Thus, Number of proton $=13$ and number of neutron $=14$

Quartz, an abundant ingredient in sand, is made up of non-crystallized silica. Silicon is neither metal nor non-metal; it's a metalloid, an element that falls somewhere between the two. Silicon is a semiconductor, meaning that it does conduct electricity.

Atomic number of $X$ is $6$ and electronic configuration is: $2, 4$
Atomic number of $Y$ is $9$ and electronic configuration is: $2, 7$
Atomic number of $Z$ is $12$ and electronic configuration is: $2, 8, 2$
Thus $X$ has four electrons in the valence $"L"$ shell.

Atomic number of a sulphur atom $S$ is $16$. It has $6$ electrons in its outermost orbit. After gaining $2$ electrons it becomes $\mathrm{S}^{2-}$. So, now the outermost orbit will have $8$ electrons.

Aluminium atom has $13$ protons and $13$ electrons.
$K L M$
Therefore, Electronic configuration of ${ }_{13} \mathrm{AI} = 2, 8, 3$

Rutherford used α-particles for scattering experiment. The $\alpha$−particles are Helium nuclei ($\mathrm{He}^{2+}$). Thus the answer for given question is Helium nuclei.

The total number of electrons present in oxygen is $8.$
Therefore, for $O$ electron configuration will be $1 s^2 2 s^2 2 p^4$.
The distribution of electrons in oxygen atom is given by:
First orbit or $K$ shell = $2\left(2 n^2=2 \times 1^1=2\right)$
Second orbit or $L$ shell $= 6(8 − 2 = 6)$

Given that, number of electrons in element $X = 15$ and number of neutrons $= 16$ Atomic number = number of protons = number of electrons in neutral atom $= 15$ Mass number = number of protons + number of neutrons $= 15 + 16 = 31.$

Metals and non-metals both can have valency $1.$
Metals which have $1$ valence electron and non-metals which have $7$ valence electrons, have valency $1$. It is because, metals loose their 1e“ and non-metals gain $1e“$ to complete their octet.

The valency shell means the outermost shell or orbit of an element which has valence electrons or outer electrons in it.
The atomic number of calcium is $20$ and its electronic configuration is $2, 8, 8, 2$ which shows that the outermost orbit or valency shell contains $2$ electrons.

Atomic no. $14$ is silicon with configuration of $2, 8, 4$ so it need four more electron to complete octet and have valency of $4.$

Magnesium ion, $\mathrm{Mg}^{2+}$ has $10$ electrons; so, its electronic configuration is $2, 8.$

Radiocarbon dating involves determining the age of an ancient fossil or specimen by measuring its carbon$-14$ content. Green plants absorb the carbon dioxide, so the population of carbon$-14$ molecules is continually replenished until the plant dies. Carbon$-14$ is also passed onto the animals that eat those plants.

Tritium $\left({ }^3 \mathrm{H}\right)$ is the only radioactive isotope of hydrogen. The nucleus of a tritium atom consists of a proton and two neutrons.

Element $X$ can’t form anions as the outermost orbit contains only $1$ electron. The atom will rather lose this electron to complete its octet and will become a cation.

Elements with valency $1$ can be either metals or non-metals. When an atom loses one electron to gain stability, it is a metal. When an atom gains an electron to complete its octet it is a non-metal.

A hydrogen atom $11HH11$ has $1$ proton and $1$ electron, but it does not have any neutron.

Rutherford experiment of scattering of $\alpha -$particles showed for the first time that the atom has a nucleus.
It is centrally located, solid, compact, small part having all positive charge and nearly the whole mass.

According to Rutherford's experiment, $\alpha −$ particles or helium nuclei impinged on a metal foil and got scattered.

Element $S$ has electronic configuration $2, 8, 6.$ It can exhibit covalency as well as electrovalency.

An atom must have a proton and an electron, but it may not have a neutron.
For example: In hydrogen atom, there is $1$ proton, $1$ electron but no neutron.

Hydrogen exists as three different isotopes. $\mathrm{H}_{-1}, \mathrm{H}_{-2}$, and $\mathrm{H}_{-3} . \mathrm{H}_{-1}$ is hydrogen with a proton in the nucleus and exists in nature as $\mathrm{H}_2$.
This is the most common form of hydrogen. $\mathrm{H}_{-2}$, also known as deuterium, has one proton and one neutron in its nucleus.
$\mathrm{H}_{-3}$, also known as tritium, has one proton and two neutrons in its neucleus. Tritium is a radioactive isotope.
So while the most common form of hydrogen has no neutrons in its neucleus, other isotopes do.

Aluminium with three valence electrons has a valency $= 3$
Fluorine has seven valence electrons and has a valency $= 1$
Magnesium has two valence electrons and has a valency $= 2$
Carbon has four valence electrons and has a valency $= 4$

Atomic number is $9$, which means that number of electrons is also $9$. Electronic configuration is $2 , 7$. So, the atom will gain $1$ electron to complete its octet. Therefore, the valency is $1$.

As the mass numbers are different, the correct option is $(c).$ They have the same number of protons.