Which compound decolourises bromine water in the absence of sunlight?
CH3CH2CH2CH3\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_3CH3CH2CH2CH3
C6H5CH3\text{C}_6\text{H}_5\text{CH}_3C6H5CH3
CH3CH=CHCH3\text{CH}_3\text{CH}=\text{CH}\text{CH}_3CH3CH=CHCH3
CH3CH2CH2CH2OH\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{OH}CH3CH2CH2CH2OH