Which chemical formula represents butane?

The correct answer represents butane, which is a straight-chain alkane with four carbon atoms. Butane's chemical formula is derived from the need to represent all four carbons connected by single bonds, adhering to the general alkane formula of CnH2n+2, where n is the number of carbon atoms.

In the case of butane, there are four carbons (n=4), leading to the formula C4H10. By examining each of the molecular structures presented, the one that corresponds to butane's composition is CH₃CH₂CH₂CH₃. This structure demonstrates that there are four carbon atoms connected in a linear fashion, fulfilling the definition of a straight-chain alkane, with the hydrogen atoms attached according to the tetravalency of carbon.

The other choices do not reflect the correct structure or number of carbon atoms for butane, making them invalid representations. Hence, the formula CH₃CH₂CH₂CH₃ accurately represents butane as a four-carbon alkane.