The correct answer is 3 which needs to be understood in two parts - Assertion (A) and Reason (R).

Assertion (A) states: "The boiling point of water decreases as the altitude increases". This is true because as altitude increases, atmospheric pressure decreases, and thus boiling point of water decreases. This happens because at higher altitudes, there`s less atmospheric pressure pushing down on the water to keep it in a liquid state. Hence, it takes less heat energy to bring water to a boil.

Reason (R) states: "The atmospheric pressure increases with altitude". This is false because it`s actually the opposite - atmospheric pressure decreases with increase in altitude. This is due to the fact that at higher altitude, fewer air molecules are present, hence the weight i.e. pressure exerted by air decreases.

Hence, A is true but R is false. So, option 3 is the correct answer.