Answer
Molecular formula is $C_{4}H_{12}N_{2}$.
Work Step by Step
Strategy: 1- Find the empirical formula mass.
2- by dividing molecular mass with empirical formula mass, we can find the number that empirical formula mass must be multiplied to find the molecular formula.
The empirical formula mass for $C_{2}H_{6}N$ :
12x2 + 1x6 + 1x14 = 44 amu
We are given the molecular mass of compound range from 87 to 90 amu. So the molecular mass is around 88.5 amu ( $\frac{87+88+89+90}{4}$ ).
We can now find the number empirical formula mass must be multiplied to find the molecular mass:
n = $\frac{Molecular mass}{empirical (formula-mass)}$
n = $\frac{88.5}{44}$ = 2.02 or n = 2 ( within experimental error)
So molecular formula should be $(C_{2}H_{6}N)_2$.
Therefore molecular formula is $C_{4}H_{12}N_{2}$.