During the melting of a slab of ice at 273 K at atmospheric pressure

There is a decrease in volume during melting on an ice slab at 273K. Therefore,
negative work is done by ice-water system on the atmosphere or positive work is
done on the ice-water system by the atmosphere. Hence option (b) is correct.
Secondly heat is absorbed during melting (i.e $\mathrm{\Delta }Q$ is positive) and as we have seen,
work done by ice-water system is negative $(\mathrm{\Delta W}$ is negative). Therefore, from first
law of thermodynamics $\mathrm{\Delta U}=\mathrm{\Delta Q}-\mathrm{\Delta W}$.

Change in internal energy of ice-water system, $\mathrm{\Delta U}$ will be positive or internal
energy will increase