I think isobutane is more stable. The reactivity of n-isobutane was analyzed. The greater the activity, the worse the stability. There are often two kinds of reactions between the two. One is substitution, that is, hydrogen on carbon is replaced by halogen; The second is fracture reaction, that is, carbon-carbon bond fracture or carbon-hydrogen bond fracture. The structure of n-butane is CH3CH2CH2CH3, and that of isobutane is (CH3)3CH. When substitution occurs, the hydrogen on tertiary carbon is most easily substituted, followed by secondary hydrogen and then primary hydrogen. Although isobutane has tertiary hydrogen, it is only 1, and the other nine hydrogens are all primary hydrogen. However, n-butane has four secondary hydrogens and six primary hydrogens, and the overall substitution trend is higher than that of isobutane (when secondary hydrogen competes with tertiary hydrogen, secondary hydrogen wins by number, and tertiary carbon is surrounded by three methyl groups, so the probability of collision with halogen decreases). When C-C bond-breaking reaction occurs, straight-chain hydrocarbons are easier than branched-chain hydrocarbons, so the yield of straight-chain hydrocarbons is higher when industrial hydrocarbons are pyrolyzed to produce low-carbon olefins. To sum up, n-butane is more reactive, that is, isobutane is more stable.