Why may bluish violet be more suitable than reddish violet for a night scene?

Correct answer: It gives a cooler effect

The governing concept is colour temperature and its effect on mood. A violet shifted toward blue is generally perceived as cooler, and cool colours can suggest night, shadow, distance and quietness. Thus option A is the best answer. Reddish violet would move toward a warmer impression; violet is not a primary colour, and a bluish shift does not necessarily make it lighter in value.