What's the next in the series?

H, Be, F, S, Mn, Kr, In, Gd, Tl, ?

John enters a small room. The Door Closes.
When the door opens, John is in a larger room.

Explain?

Can you find the number of triangles in the given figure?

Which alphabet letter is a question?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

A seven-year-old kid challenged his classmates that he can make the number one disappear by adding something to it.

How can he do that?

What do you see here? Your task is to find three words hidden in the optical illusion

There is a number which when you multiply by 3 and subtract 2 from the result, then the resulting number is the reverse of the actual number.

What is the smallest number that stands true on the statement?

You are provided with a grid (as shown in the picture). Can you fill the squares with numbers 1-8 in a manner that none of the two consecutive numbers are placed next to each other in any direction (vertically, horizontally or diagonally?)

Can you divide the below-given shape into four equal and identical pieces?