How many moles of magnesium phosphate, $\mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}$ will contain 0.25 mole of oxygen atoms?

JEE Main · 2006 · 30 Apr 2006 · Offline · Some Basic Concepts of Chemistry

How many moles of magnesium phosphate,

Mg_{3} (PO_{4})_{2}

will contain 0.25 mole of oxygen atoms?

Answer: (B)

One formula unit of

M g_{3} (P O_{4})_{2}

carries two phosphate groups, and each phosphate holds four oxygen atoms, so there are eight oxygen atoms per formula unit. If

n

moles of the salt are taken, the oxygen atoms amount to

8 n

moles. Setting

8 n = 0.25

gives

n = 0.25/8 = 3.125 \times 1 0^{- 2}

moles of magnesium phosphate.

JEE Main · 2006 · 30 Apr 2006 · Offline · Single correct option