Question

The percentage composition of $Cr$ in $K _{2} Cr _{2} O _{7}$ is_________ $\%$.
(At. mass: $K=39\, u ; Cr=52\, u ; O=16\, u$ )

Answer 1

Molar mass of $K _{2} Cr _{2} O _{7}$
$=2 \times(39)+2 \times(52)+7 \times(16)$
$=78+104+112=294\, g\, mol ^{-1}$
Percentage of $Cr =\frac{104}{294} \times 100=35.37 \%$