2011-AL-CHEM 1 Q.2(a)(i)

What're your difficulties?

first, Cr comes from the central atom of the complex ion, in 1-to-1 ratio.

next, S comes from only the -NCS ligand. mole of this compound has x mole of -NCS ligand, and thus x mole of S atoms.

then, N comes from the ammonium ion, -NCS ligand as well as the -NH3 ligand. in 1 mole of compound, there's 1 mole of ammonium ion (providing 1 mole of N), x mole of -NCS ligand (providing x mole of N) and y mole of -NH3 ligand (providing y mole of N).
thus, total no. of mole of N in 1 mole of compound
= 1*1 + x*1 + y*1 = (1+x+y) mole

mole ratio of Cr : S : N = 1 : x : (1+x+y)