Question 1

Electron affinity is positive, when

Accepted Answer

When O ^ - changes into O ^ 2- , energy is absorbed i.e the change is endothermic because O ^ - repels the incoming electron due to similar charge. H ice, it needs energy to add (accept) the electron. So, electron affinity ( EA _2 ) is positive.

Question 2

The ionic radii in (Ã…) of N ^ 3- , O ^ 2- and F ^ - are respectively.

Accepted Answer

N ^ 3- , O ^ 2- and F ^ - are isoelectronics ( 10 electrons) species. Their ionic radii will decrease with increase in magnitude of the nuclear charge from N ( Z =7) to O (Z=8) and F(Z=9). i.e. array ccc N ^ 3- & O ^ 2- & F ^ - \ 1.71 Ã… & 1.40 Ã… & 1.36 Ã… array Hence, option (1) is correct.

Question 3

How many elements are there in 6^ th period of periodic table?

Accepted Answer

6^ th period consists of 32 elements.

Question 4

Element with electronic configuration 1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 3 d^ 10 4 s^2 4 p^6 4 d^ 10 5 s^2 5 p^3 belongs to the following group of the periodic table

Accepted Answer

Its valence shell has 5 electrons (n s^2, n p^3 ) It belongs to 15 th group of the periodic table.

Question 5

The correct order of acidic strength :

Accepted Answer

Acidic character of oxide Non-metallic nature of element. Non-metallic character increases along the period. Hence order of acidic character is Cl _ 2 O _ 7 > SO _ 2 > P _ 4 O _ 10

Question 6

Arrange the following ions in the order of decreasing X - O bond length, where X is the central atom

Accepted Answer

More will be the electronegativity of X lesser will be the bond length of X - O bond.

Classification of Elements and Periodicity in Properties — Previous Year Questions & Solutions