Classification of elements and Periodicity in properties MCQs for NEET — Chemistry Questions with Answers

radius decreases from left to right in P.T

IE$\propto \mathrm{O}.\mathrm{S}$

group 15, has I.E₆ >>>>I.E ₅

n-1  = grp 17

n - 2 = grp 16

n + 1 = grp 1

n + 2 = grp 2

so grp 17  will have highest I.E

Addition of 2nd electron is always endothermic.

(a)

For option (a)

First ionisation energy is the energy required to remove an electron from outermost shell.

Hence, correct order is B < C < O < N.

For option (b)

Electron gain enthalpy is the energy required to gain an electron in the outermost shell.

Hence, the correct order is I < Br < F < Cl.

For option (c)

As we move down the group in alkali metal, metallic radius increases Li < Na < K < Rb.

For option (d)

In case of isoelectronic species, as positive charge decreases or negative charge increases the ionic size of the species increases and vice-versa Al³⁺ < Mg²⁺ < Na⁺ <F^- .

            Ca²⁺ < K⁺ < Ar
Ar , K⁺ and Ca²⁺ are isoelectronic i.e. with same number of electrons. 18. For isoelectronic species ionic radii decreases with increase in effective (relative) positive charge. Also Ar, K and Ca belong to the same period (3rd period).

(a) Since, electron repulsion predominate over the stability gained by achieving noble gas configuration. Hence, fomation of O^2- in gas phase is unfavourable.