What goes up but never comes down?

What is the end of everything?

What you cannot hold but it is yours?

What always comes into a house through the keyhole?

Find the hidden panda in the image below.

What brings you down but never up?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

Suppose you are sitting in an interview and the interviewee asks you an aptitude question.

You have three buckets with a capacity of 4 litres, 8 litres and 10 litres and you have a large tank of water. Now you have to measure 3 litres of water precisely using those buckets. How will you do it?

What is the coolest letter in the alphabet?

The following four words might seem abrupt to you. But you can make them meaningful by just adding vowels.
RDSH
GGPLNT
TMT
NN

Hint: All of them are vegetables.