Which of the following equation is a double replacement reaction?
(A) C(s) + O2(g) -> CO2(g)
(B) Fe(s) + H2S(g) -> FeS(s) + H2(g)
(C) BFe(s) + S8(s) -> 8FeS(s)
(D) NaCl(ag) + AgNO3(aq) -> AgCl(s) + NaNO3(aq)

A double replacement means there are 2 replacements going on, which one do you think it is? :)

Which of the following equation is a double replacement reaction?
(A) C(s) + O2(g) -> CO2(g)
(B) Fe(s) + H2S(g) -> FeS(s) + H2(g)
(C) BFe(s) + S8(s) -> 8FeS(s)
(D) NaCl(ag) + AgNO3(aq) -> AgCl(s) + NaNO3(aq)

If you're in year 11 or an A-level student, I suggest you re-read your notes. For a double replacement to happen, there must be a significant difference to both sides of the equation.

Two compounds must NOT be identical on both sides of the equation. With that information, it's straight forward to choose the correct one, there's no need to go into a long winded chemical explanation.