Which of the following choices would have a negative entropy change?

A. N2(g) + 3H2(g)- >2NH3(g)
B. CaCO3(s) – > CaO(s) + CO2(g)
C. H2O(s)-> H2O(l)
D. Fe2O3(s) + 3C(s)- > 2Fe(s) + 300(g)

N2(g) + 3H2(g)- >2NH3(g) denotes a negative entropy change.

Entropy is defined as the extent of disorder in a system. The degree of entropy is more in a gas and less in a solid.

Here, 1st reaction produces ammonia from nitrogen and hydrogen. We can see that four moles of gases produces 2 moles of gaseous product. So the degree of disorder in the system is decreasing. So the entropy is also decreasing.

it is the most commonly accepted one

i think it's letter a.