The correct option is A +ve
In the reaction,
MgCO3(s) decomposes to give MgO(s) and CO2(g).
Entropy of gases is more than that of solids and liquids.
Entropy increases when there is an increase in the number of moles (gaseous) on the product side i.e., when △ng>0
nP= total number of gaseous moles of products
nR= total number of gaseous moles of reactants
So, the value of Δng=1−0=1
Thus, entropy increases.