Atomicity of dimeric phosphorous pentoxide is ‘x’ and the number of shared electron pairs is ‘y’. Then
a) y – x = 6            b) 2x = y + 8           c) 10x – 7y = 0

Dimer of phosphorus pentoxide is P₄O₁₀ and its atomicity is 14 (x=14). In P₄O₁₀, each P forms 5 bonds with neighboring atoms, this means that each P shared 5 electron paired and as their are 4 P atoms, hence value of y=20.

$$\begin{gathered} \mathrm{a}) \mathrm{y} – \mathrm{x} = 6 \\ 20-14=6 \left(\mathrm{a} \mathrm{is} \mathrm{correct}\right) \\ \mathrm{b}) 2\mathrm{x}=\mathrm{y}+8 \\ 2\left(14\right)=20+8 \\ 28=28 \left(\mathrm{b} \mathrm{is} \mathrm{correct}\right) \\ \mathrm{c}) 10\mathrm{x}-7\mathrm{y}=0 \\ 10(14)-7(20)=0 \\ 140-140=0 \left(\mathrm{c} \mathrm{is} \mathrm{correct}\right) \end{gathered}$$