Answer
The formula of the molecular compound is $C_{2}H_{4}$.
Work Step by Step
The atomic mass unit (amu) for the compound $C_{2}H_{4}$ is roughly 28.04 amu because $(2*12.00 + 4*1.01 = 28.05)$ which closely matches the atomic mass of the compound given in the question (28.06 amu). Since the compound only contains carbon and hydrogen as stated in the question, the only possibility is ethene $(C_{2}H_{4})$ which is a different form of ethane with two less hydrogen molecules due to the double bond between the carbon atoms.