$15{ \mathrm{cm}}^3$ of liquid $\text{'} \mathrm{x} \text{'}$ and $20{ \mathrm{cm}}^3$ of liquid $\text{'} \mathrm{y} \text{'}$ are mixed at $20°\mathrm{C}$ and the volume of solution was measured to be $35.1{ \mathrm{cm}}^3$then correct reaction is

For x

${\mathrm{V}}_{\mathrm{x}}=15{\mathrm{cm}}^3$

For y

${\mathrm{V}}_{\mathrm{y}}=20{\mathrm{cm}}^3$

Now,

${\mathrm{V}}_{\mathrm{x}}+{\mathrm{V}}_{\mathrm{y}}=15+20=35{\mathrm{cm}}^3$

Which is less than the observed volume.

$35<35.1$(observed volume)

i.e., $∆ \mathrm{V} = 0.1$

As $∆ \mathrm{V} >0$ it means $∆ \mathrm{V}$is positive,

We know that if $∆ \mathrm{V}$ is positive it will show a positive deviation.

Hence, $∆ {\mathrm{H}}_{\mathrm{mix}}>0$ ,the solution shows a positive deviation.

Therefore, option(b) is correct.