A gaseous hydrocarbon contains $85.7 \%$ carbon and $14.3 \%$ hydrogen. 1 litre of the hydrocarbon weighs 1.26 g at NTP? Determine the molecular formula of the hydrocarbon.

Hint: The number of atoms of the elements in one molecule of a chemical is expressed by the molecular formula. The formula that displays the precise number of each atom in a molecule is known as a molecular formula. The Molecular Method is determined using the empirical formula when the molar mass value is known.

Formula Used $n=$molar mass/the empirical formula's mass
The empirical formula or an exact multiple of it, as well as the molecular formula, are frequently the same.

Complete Step by Step Solution:
Mole ratio of Carbon : Hydrogen
$=\dfrac{85.7}{12}: 14.3$
$=7: 14=1: 2$
While the molecular formula provides the precise quantity of each unique element present in a molecule, the empirical formula of a compound provides the simplest ratio of the number of various atoms present. It is an empirical formula if it has been simplified. The empirical formula is multiplied by the widely used molecular formula.
Empirical formula $=\mathrm{C}_{\mathrm{n}} \mathrm{H}_{2 \mathrm{n}}$ : empirical formula wt $=14$
Given 1 litre at NTP weighs $1.26 \mathrm{~g}$
Therefore 22.4 litres will weigh $\dfrac{22.4}{1.26}=28 \mathrm{~g}$
$\mathrm{n}=\dfrac{28}{14}=2$
so the required formula is $\mathrm{C}_{2} \mathrm{H}_{4}$

Note: The empirical formula, which is defined as the ratio of subscripts of the least whole number of the elements present in the formula, is the simplest formula for a compound. The simplest formula is another name for it. The formula of a material expressed with the smallest integer subscript is referred to as an empirical formula for a compound. The empirical formula provides details regarding the ratio of atom counts in the molecule. A compound's empirical formula is directly related to its % content.