Question

The molecular mass of the molecule of a phosphorus compound $P_2{X}_5$ is 142 g. The atomic mass of phosphorus is 31 g. What will be the molecular mass of compound $N_2{X}_4$?

• A. 112
• B. 92
• C. 108
• D. 86

Answer 1

The correct option is B 92

• Let’s start with $P_2{X}_5$,
• Molecular mass = 2 (Atomic mass of P) + 5(Atomic mass of X)
• 142 = 2(31) + 5(Atomic mass of X)
• Atomic mass of X = 16
• Element X is oxygen.
• Thus, the Chemical formula would be $P_2{O}_5$
• Therefore, $N_2{X}_4$ would be $N_2{O}_4$
• Let’s calculate the molecular mass of $N_2{O}_4$.
  Molecular mass = 2(Atomic mass of N) + 4(Atomic mass of O)
  Molecular mass = 92 g
  Thus, the Molecular mass of $N_2{0}_4$ is 92 g.