Chemistry M.C.Q (1 Marks)

Hydrogen experiences the maximum effective nuclear charge. After removal of a electron there will be no electron in the species. Just a nucleus with positive charge will be left which is very unstable. Therefore, ionization potential is maximum for hydrogen.

After losing one electron, it acquires stable electronic configuration, that is why second ionisation enthalpy is very high.

Explanation: (C) Decreases
The higher the metal in the series, the more reactive it is and the more vigorously it reacts with water, oxygen and acid. A metal in the activity series can displace any metal below it in the series from its compound. The elements potassium, sodium, lithium and calcium are very reactive and they react with cold water to produce hydroxides and hydrogen gas. The metals above hydrogen are more reactive than hydrogen. These metals can displace hydrogen from acids or water and liberate hydrogen gas. The metals copper, silver gold and platinum are less reactive than hydrogen and they do not replace hydrogen from water or acid.

Helium, xenon and radon are inert gases. Radium is an alkaline earth metal.

C. Potassium

Explanation: Sodium Na and Potassium K are present in the group I that is alkali metal elements. While Magnesium Mg and Calcium Ca are group II alkaline earth metals. As we move from left to right in the periodic table the ionization energy increases as new electrons enter the same shell so, effective nuclear charge increases. So, Na and K are more reactive than Mg and Ca respectively. And as we go down the group number of shells increases so atomic size increases so, ionization energy decreases. As ionization energy decreases the reactivity of metal increases. So, Potassium is the most reactive metal.

Since, it has two valence electrons, it is a part of alkaline earth metals, therefore, it is a metal.

A qualitative measure of the ability of an atom in a chemical compound to attract shared electrons to itself is called electronegativity. Unlike ionization enthalpy and electron gain enthalpy, it is not a measureable quantity.

Similar outer configuration in their atoms are arranged in vertical columns called groups or families.

Boron and silicon resemble chemically. This is due to the equal value of their ion's polarizing power.
This chemical resemblance is called diagonal relationship. It is due to similarity in ionic sizes and charge/radius ratio of elements.

It has largest atomic size.

Mendeleev arranged elements in horizontal rows and vertical columns of table in the order of their increasing atomic weights.

Introduction to Mendeleev's Periodic table:
The pair of the element in the periodic table where the element occurring before has more atomic mass than the later occurring one. It is also considered to be a drawback of Mendeleev’s periodic table.
Reasons of anomalous :
The size of an atom is less
Electronegativity is very high as a result ionization enthalpy increases.
The charge to radius ratio is large.
The below image shows the anomalous pairs of elements in Mendeleev's periodic table;

Neutron to proton ratio is not a periodic property as it is not having any regular trend where as the remaining options have a regular trend in groups as well as periods.

Chlorine, oxygen and silicon were included in Mendeleev's periodic table. Germanium was discovered later which fit into the empty spaces left by Mendeleev and matched to the expected properties.

According to Mendeleevs classification, the properties of elements are the periodic function of their atomic masses and there is a periodic recurrence of elements with similar physical and chemical properties.
Noble gas being inert, could be placed in a separate group without disturbing the original order.

In Isoelectronic species, higher the nuclear charge, smaller the size.

A diagonal relationship exists between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table.

The elements of first and second groups, i.e., alkali and alkaline earth metals possess low ionization energies and impart colour to the flame.

Among the given metals, Caesium has the lowest ionization enthalpy.
Hence, it loses electrons readily.

The metallic character is used to define the chemical property that metallic elements present. Generally, metals tend to lose electrons to form cations. Nonmetals tend to gain electrons to form anions.
They also have a high oxidation potential therefore they are easily oxidized and are strong reducng agents.
Thus the property which regularly increases down the group in the periodic table is Reducing nature.

The size of the atom increases as reflected in the van der Waals' radius.

Atomic radius decreases as we move from left to right in a period in the periodic table. Fluorine has the smallest atomic radius. As we move to neon in the same period, the atomic radius increases as it has van der Waals radius and van der Waals radii are bigger than covalent radii.

The atomic radius refers to the size of an atom.
It is the distance between the centre of the nucleus and the outermost shell of an atom.
Atomic radius generally decreases on moving left to right across a period and increases down the group.

Larger the anion, more will be the polarizing power.

It has positive electron enthalpy due to stable electron gain enthalpy, there is repulsion between electron to be added and valence electrons.

Beryllium and aluminum shows diagonal relationship with each other.
Hence, they exhibit similar properties.

Boron and silicon are both semiconductors, form halides that are hydrolysed in water and form acidic oxides. Boron and silicon have diagonal relationship.

On moving down the halogen group, the atomic radius, ionic radius and the boiling point increases with an increase in the atomic number. However, ionisation potential decreases. The effect of an increase in the atomic size and the shielding effect is much more than the effect of the increase in nuclear charge.
Hence, the electron becomes less and less firmly held to the nucleus on moving down the group. Hence, the ionization potential gradually decreases on moving down the group.

Mendeleev kept elements in increasing order of atomic weights in seven periods and eight groups.

This requires highest energy to lose four electrons.

Noble gases have very stable configuration. It is not easy to remove an electron from such a stable configuration. Thus, noble gases have the highest ionization potential in a particular group.
Therefore, among the given options argon has the highest ionization potential.

Atomic radius decreases from left to right in a period and increases from top to bottom in a group.
Similarly, the negative value of electron gain enthalpy decreases in a period and increases in a group.
So Atomic radius and electron gain enthalpy show reverse properties on moving along a period from left to right and in the group from top to bottom.