Complete the table series riddle by finding the number that can replace "??".

How can you take 2 from 5 and leave 4?

Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??

How many Watermelons are there in the below picture?

what does this below rebus represent identXQQQQQME

It belongs to you, but other people use it more than you do. What is it?

John: "Hi Teacher, What is your favourite movie ?".
Chemistry Teacher: "Indium Cerium Platinum Iodine Oxygen Nitrogen".
Ten seconds later... John replied I got it.

Do you?

The dirtier I get, the whiter I look. Who am I?

A number can be multiplied by multiple of nine
i.e 9 18 27 36 45 ...

and the resulting number consist of only one digit.

Can you identify the number ?

I am the black child of a white father, a wingless bird, flying even to the clouds of heaven. I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth, I am dissolved into air. What am I?