According to Charles' Law the volume of an ideal gas is directly proportional to its absolute temperature in Kelvin keeping the pressure constant.
V∝ T, P is constant
where V, T and P are volume, temperature and pressure
= 
where V₁, T₁, V₂ and T₂ are initial volume, initial temperature, final volume and final temperature.
The correct answer is option 1. Butane and 2-butene have the same total number of carbon atoms. They both have four carbon atoms. They differ in there structure since the latter has double bonds on it. As a result of the different structure, they also have different properties.
"The water becomes warmer."
<u>Remember</u>: Kinetic energy means how much, on average, a molecule is moving around. This is directly translated into heat. Therefore, the higher the kinetic energy, the more heat produced.