Count, for one molecule each of P4O6 and P4O10, the P-O-P linkages in both molecules together with the P=O bonds in P4O10. The total is

JEE Advanced levelSingle correct optionDifficulty 3 of 3pn217

Count, for one molecule each of $P X_{4} O X_{6}$ and $P X_{4} O X_{10}$ , the P-O-P linkages in both molecules together with the P=O bonds in $P X_{4} O X_{10}$ . The total is

P X_{4} O X_{6}

has 6 P-O-P bridges and no P=O.

P X_{4} O X_{10}

keeps the same 6 bridges and adds one terminal P=O per P atom, 4 in all. Total

= 6 + 6 + 4 = 16