Answer
a)
:
= +ve
b)
:
= -ve
c)
:
= +ve
d)
:
= +ve
Explanation:
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.