All i know that we are HOOman
Answer is: formula of the complex is [Cr(NH₃)₂(SCN)₄<span>]</span>⁻<span>.
This complex has negative charge (-1) because chromium (central atom or metal) has oxidation number +3, first ligand ammonia has neutral charge and second ligand thiocyanate has negative oxidation number -1:
+3 + 2</span>·0 + 4·(-1) = -1.
2 H₂ + O₂ = 2 H₂O
Answer B only synthesis.
hope this helps!
1/15 is the correct answer I think