Which one the following has largest number of isomers? (R = alkyl group, en = ethylenediamine)

Coordination compound have great importance in biological systems. In this context which of the following statements is incorrect?

The coordination number of central metal atom in a complex is determined by :

6.02 $$\times$$ 10²⁰ molecules of urea are present in 100 ml of its solution. The concentration of urea solution is
(Avogadro constant, N_A = 6.02 $$\times$$ 10²³ mol^-1)