Number of electrons present in 4f orbital of Ho³⁺ ion is ____________. (Given Atomic No. of Ho = 67)

Consider the above chemical reaction. The total number of stereoisomers possible for Product 'P' is _____________.

For a chemical reaction A $$\to$$ B, it was found that concentration of B is increased by 0.2 mol L^$$-$$ in 30 min. The average rate of the reaction is ____________ $$\times$$ 10^$$-$$1 mol L^$$-$$1 h^$$-$$1. (in nearest integer)

Assuming that Ba(OH)₂ is completely ionised in aqueous solution under the given conditions the concentration of H₃O⁺ ions in 0.005 M aqueous solution of Ba(OH)² at 298 K is ______________ $$\times$$ 10^$$-$$12 mol L^$$-$$1. (Nearest integer)