Question

In which one of the following arrangements the given sequence is not strictly according to the properties indicated against it?

• A. $HF < HCl < HBr < HI$ : Increasing acidic strength
• B. $H _{2} O < H _{2} S < H _{2} Se < H _{2} Te$ : Increasing $pK_{a}$ values
• C. $NH _{3}< PH _{3} < AsH _{3}< SbH _{3}$ : Increasing acidic character
• D. $CO _{2}< SiO _{2} < SnO _{2}< PbO _{2}$ : Increasing oxidizing power

Answer 1

Answer: (B)

From $H _{2} O$ to $H _{2}$ Te as $X - H$ bond enthalpy decreases, acidic strength increases ( $K _{ a }$ increases)
$\therefore H _{2} O < H _{2} S < H _{2} Se < H _{2} \text { Te....K } K _{ a } $
$ H _{2} O > H _{2} S > H _{2} Se > H _{2} \text { Te....P }^{ K _{ a }}$