The correct descending order of the heat liberated (in kJ) during the neutralisation of the acids `CH_(3)COOH(W), HF(X), HCOOH(Y)` and HCN (Z) under identical conditions (`K_(a)` of `CH_(3)COOH = 1.8 xx 10^(-5), HCOOH = 1.8 xx 10^(-4), HCN = 4.9 xx10^(-10)` and `HF = 3.2 xx 10^(-4)`) is

Options

A. `Y gt X gt Z gt W`
B. `X gt Y gt W gt Z`
C. `W gt X gt Y gt Z`
D. `Z gt W gt Y gt X`

Answer

B

Explanation

Given,
`K_(a)` for `CH_(3)COOH = 1.8 xx 10^(-5) (W)`
`K_(a)` for `HCOOH = 1.8 xx 10^(-4)(Y)`
`K_(a)` for `HCN = 4.9 xx 10^(-10)(Z)`
and `K_(a)` for `HF = 3.2 xx 10^(-4)(X)`
Now, `because K_(a) prop` Strength of acid
or, `K_(a) prop` Heat liberated during neutralisation
Thus, order of heat liberated during neutralisation is
`HF gt HCOOH gt CH_(3)COOH gt HCN`
i.e. `X gt Y gt W gt Z`