What is the value of spin only magnetic moment for $\text{Cu}^{2+}$ in BM?

The sum of coordination number and oxidation number of M in $[\text{M(en)}_2\text{C}_2\text{O}_4]\text{Cl}$ is

In the coordination complex, Potassium hexacyanoferrate(II), the central atom/ion acts as,

Which of the following halogen derivative forms a poisonous phosgene, when come in contact with air and light?