Question

Which of the following statements related to VA group hydrides are true?
I. Reducing property increases from NH${}_3$ to BiH${}_3$
.
II. Tendency to donate lone pair decreases from NH${}_3$ to BiH${}_3$
.
III. Ease of replacing H with Cl decreases from NH${}_3$ to BiH${}_3$
IV. Ease of formation of hydrides decreases from NH${}_3$ to BiH${}_3$

• A. I, II, III and IV
• B. I, III and IV
• C. I, II and IV
• D. I and IV

Answer 1

The correct option is A I, II, III and IV

The hydrides show regular gradation in their properties.
The stability of hydrides decreases from $N{H}_3$ to $Bi{H}_3$ due to increase in bond length between two atoms Down the group size increases and overlap decreases so the bond strength increases. Hence their bond dissociation enthalpy decreases.
Consequently, the reducing character of the hydrides increases.
Ammonia is only a mild reducing agent while $Bi{H}_3$ is the strongest reducing agent amongst all the hydrides. Basicity also decreases in the order $N{H}_3>P{H}_3>As{H}_3>Sb{H}_3>Bi{H}_3$.
Down the group size increases and the lone pair got stabilized on the big surface area of atom.
Down the group the basicity decreases and hence the ease of replacing H with Cl decreases.