Questions

For an atom to emit X-rays it should have difference in energy levels

Kachchh district is the largest in India in terms of territorial extent, located in the state of Gujarat.
The second largest district is Leh in Jammu & Kashmir.

Envelope is a letter holder for one letter and in the question it mean that it holds one letter. Eye is also a word which starts and end with E but has one letter in the middle.

A skid happens whenever the tires lose their grip on the road. Braking skids occur when the brakes are applied so hard that the front or rear wheels lose traction.