In the photograph of Titania, why is half the moon in darkness?

Mercury takes $59$ Earth days to spin once round its axis.

Are the nights and days longer or shorter than on Earth?

Which of these is a star and which is a planet in the below-given picture?

Define orbit.

Here are the times it takes two planets to orbit the Sun:

A: $88$ Earth days. B: $29.5$ Earth years.

Which planet, A or B, is Mercury? Explain why.