Answer
The bonding in methane, ethane, propane and butane consists of only sigma ($\sigma$) bonds, with the bonds around each Carbon atom having tetrahedral geometry. Each Carbon atom is $sp^3$ hybridized.
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The formulas for all these compounds can be simplified to the general formula: $C_{n}H_{2n+2}$, where $n$ is the number of carbon atoms.
Each compound differs by one $CH_2$ group, i.e., the value of n.
Work Step by Step
Methane, ethane, propane and butane all fall under the functional group of $alkanes.$ They are known as $saturated\space hydrocarbons$.
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For Methane, n = 1 $\implies$ $C_{n}H_{2n+2} = CH_4$
For Ethane, n = 2 $\implies$ $C_{n}H_{2n+2} = C_{2}H_6$
For Propane, n = 3 $\implies$ $C_{n}H_{2n+2} = C_{3}H_8$
For Butane, n = 4 $\implies$ $C_{n}H_{2n+2} = C_{4}H_{10}$
