The reaction with bromine water indicates the presence of unsaturated bonds. Alkanes, being saturated hydrocarbons, do not react with bromine water under these conditions. Therefore, the hydrocarbon that will not decolorize bromine water is a saturated one. Among the given options, 'бутан' (butane) is a saturated hydrocarbon (alkane). The other options, 'пропен-1' (propene-1), 'этин' (ethyne), and 'бутадиен-1,3' (butadiene-1,3), all contain double or triple bonds and would react with bromine water.
Answer: а) бутан