One s orbital and one p orbital of silver mix and undergo sp hybridization to form two hybrid orbitals which overlap with appropriate orbitals of two ammonia molecules.
Hence the correct option is B.
$A: \left[ Ni ( en )_{3}\right]^{2+}, B :\left[ Ni \left( NH _{3}\right)_{6}\right]^{2+}, C :\left[ Ni \left( H _{2} O \right)_{6}\right]^{2+}$
$\left( {{C_2}O_4^{2 - } = } \right.$ ઓક્ઝલેટો $)$