Entropy is the measure of randomness or disorder of a system. If a system moves from an ordered arrangement to a disordered arrangement, the entropy is said to decrease and vice versa.
a)
As solid is moving to ions form , randomness increases and thus sign of is positive.
b)
As gaseous reactants are converted to solid products , randomness decreases and thus sign of is negative.
c)
As liquid is changing to gas randomness increases and thus sign of is positive.
d)
As 8 moles of gaseous reactants are converted to 11 moles of gaseous products , randomness increases and thus sign of is positive.