Hii..

Entropy is basically an increase in randomness of a system. In other words, an increase in entropy suggests that your ability to predict behavior of the particles involved is decreasing.

At 373K (during evaporation), the energy absorbed by water molecules is used up to break intermolecular bonds and hydrogen bonds. So, the particles dont really start moving more randomly. Hence, the change in randomness, or entropy, is zero.

Thanks..!!