What word begins and ends with an E, but has only one letter?

Can you solve this picture maths equation?

The more of this there is, the less you see. What is it?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

My thunder comes before the lightning; my lightning comes before clouds; my rain dries all the land it touches. What am I?

Manish has to secure 40% marks to pass his B.tech final exams.
He got just 40 marks and failed by 40-marks.

What is the maximum marks?

I hide my treasure in the ground, my tail is big and fluffy. If you spot me in a tree, please don’t call me scruffy. What am I?

He does not have any heart but still, He manages to live.
If you kill him, you will eventually die but yet you kill him.
He cannot run, who is He?

What breaks yet never falls, and what falls yet never breaks?

I go up and I go down.
I go up towards the beautiful sky and down toward the green ground.
I am present tense.
I am past tense too
Children love me.

Who Am I?