A compound has the molecular formula $X_4{O}_6$ . If 11 g of $X_4{O}_6$ has 6.2 g of X, then what is the atomic mass of X?

Let 'a' be the atomic mass of the element X and the atomic mas of oxygen is 16, Hence, the total molecular weight can be written as:

$Molecularweightif{X}_4{O}_6==4a+6\times 16=4a+96$

$(4a+96)gramof{X}_4{O}_{6}containsX=4agram$

$11gramof{X}_4{O}_{6}containsX=4a\times \frac{11}{4a+96}$

$6.2grams=4a\times \frac{11}{4a+96}$

$24.8a+595.2=44a$

$19.2a=595.2$

$a=\frac{595.2}{19.2}$

$a=31amu$

Hence the atomic mass of X = 31 amu

, Hence the element X is phosphorous. So the chemical formula is $P_4{O}_6$