Both statements I and II are individually true. Statement I correctly states that the Doldrums is a low pressure area around the Equator where the prevailing winds are calm. This region is characterized by light winds and variable weather conditions, making it challenging for sailors to navigate through.
Statement II provides an explanation for the low pressure in the Doldrums. It states that the low pressure is caused by the heat at the Equator, which makes the air rise and travel both northwards and southwards. As the air rises, it creates a vacuum at the surface, leading to lower pressure.
Therefore, it can be concluded that Statement II is the correct explanation of Statement I. The intense heating of the Equator causes the air to rise, creating a low pressure area in the Doldrums. This low pressure zone is responsible for the calm winds and unstable weather conditions observed in the Doldrums region.