What is the molecular formula for butane?

Butane is an alkane with the general molecular formula ( C_nH_{2n+2} ), where ( n ) represents the number of carbon atoms in the molecule. For butane, ( n ) is 4, which results in a molecular formula of ( C_4H_{2(4)+2} ). This calculation leads to ( C_4H_{10} ), confirming that the molecular formula for butane is indeed ( C_4H_{10} ).

The other choices presented do not adhere to the alkane formula. ( C_4H_9 ) indicates one less hydrogen than needed for an alkane, suggesting it might be a radical or an ion. Meanwhile, ( C_4H_8 ) denotes a reduction in hydrogen that aligns with alkenes or cyclic compounds, as it reflects unsaturation. ( C_3H_7 ) indicates a three-carbon molecule, which is certainly not butane but rather corresponds to a propyl radical structure. Hence, ( C_4H_{10} ) accurately represents butane as an unbranched alkane with four carbon atoms and matches the expectations of its molecular structure.