(A) Calculate the amount of calcium oxide required to react with 852 g of P$$_4$$O$$_{10}$$.

(B) Write the structure of P$$_4$$O$$_{10}$$.

An element crystallises in fcc lattice having edge length 400 pm. Calculate the maximum diameter of the atom which can be placed in interstitial site such that the structure is not distorted.

Nitrogen gas is absorbed on 20% surface sites. On heating N$$_2$$ gas evolved from sites and was collected at 0.01 atm and 298 K in a container of volume 2.46 cm$$^3$$. Find out the number of surface sites occupied per molecule of N, if the density of surface sites is $$6.023\times10^{14}/\mathrm{cm^3}$$ and surface area is 1000 cm$$^2$$.

Predict whether the following molecules are iso-structural or not. Justify your answer.

(A) NMe$$_3$$

(B) N(SiMe$$_3$$)$$_3$$