What does below chemistry rebus means?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

In The 1st month of this year(the year 2013), I noticed that the date 13-1-13 (13 January 2013) is special.

This date is special as:

Date * Month = Year.

Can you figure out which year of this century has a maximum number of such dates?

In four steps you need to move the word 'cold' From 'warm' by replacing one alphabet at a time such that every word formed at each step is acceptable in English Dictionary.

In this image, you can see three almost identical Doraemon images. Can you spot the odd one out from them?

By using 'because' continuously three times, can you make an English statement ?

Spot what is wrong here in below Picture?

Two friends were stuck in a cottage. They had nothing to do and thus they started playing cards. Suddenly the power went off and Friend 1 inverted the position of 15 cards in the normal deck of 52 cards and shuffled it. Now he asked Friend 2 to divide the cards into two piles (need not be equal) with equal number of cards facing up. The room was quite dark and Friend 2 could not see the cards. He thinks for a while and then divides the cards in two piles.

On checking, the count of cards facing up is same in both the piles. How could Friend 2 have done it ?

I have teeth but i don't bite. Who Am I ?

The day after tomorrow will be three days before Tuesday. Can you find out what is today?