Empirical Formula
The empirical formula of a compound represents the simplest whole number ratio of the atoms present in the compound. In the given problem, the empirical formula of the colourless liquid used in rocket engines is NO2.

Molecular Mass
The molecular mass of a compound is the sum of the atomic masses of all the atoms present in one molecule of the compound. In this case, the molecular mass of the compound is given as 92.

Determining the Molecular Formula

To determine the molecular formula, we need to find the actual number of atoms of each element in one molecule of the compound. We can do this by comparing the molecular mass with the empirical formula mass.

Calculating Empirical Formula Mass
To calculate the empirical formula mass, we need to find the atomic masses of the elements present in the empirical formula and add them together.

- Nitrogen (N) has an atomic mass of 14.01 g/mol.
- Oxygen (O) has an atomic mass of 16.00 g/mol.

The empirical formula mass can be calculated as follows:
Empirical formula mass = (atomic mass of N) + 2 × (atomic mass of O)
Empirical formula mass = 14.01 + 2 × 16.00
Empirical formula mass = 14.01 + 32.00
Empirical formula mass = 46.01 g/mol

Determining the Multiplier
The multiplier is the ratio of the molecular mass to the empirical formula mass. It represents the number of empirical formula units present in one molecule of the compound.

Multiplier = Molecular mass / Empirical formula mass
Multiplier = 92 / 46.01
Multiplier ≈ 2

Molecular Formula
The molecular formula represents the actual number of atoms of each element in one molecule of the compound. To determine the molecular formula, we need to multiply the subscripts of the empirical formula by the multiplier.

Molecular formula = (subscript of N in empirical formula) × multiplier + (subscript of O in empirical formula) × multiplier
Molecular formula = 1 × 2 + 2 × 2
Molecular formula = 2 + 4
Molecular formula = 6

Therefore, the molecular formula of the colourless liquid used in rocket engines is N2O4.