What has many keys but can’t open a single lock?

Can you find a five letter word that is left with only two letters if one is removed?

Can you count the number of squares in the figure below?

Prove that twice of ten is the same as twice of eleven.

How many words can a quill made with the feather of a pigeon write with a 100ml bottle of black ink?

Speaking of rivers, a man calls his dog from the opposite side of the river. The dog crosses the river without getting wet, and without using a bridge or boat. How?

In a science lab, a petri dish hosts a healthy colony of yeast for an experiment. Now every minute, all the yeast cells divide into two. At noon, there was just a single cell of yeast and at 1:22, the Petri dish was half full. Can you calculate when the dish will be full of yeast?

A train leaves from point A for point B at 80 mph. After half an hour, another train leaves from point B for point A at 60 mph.

Which of the trains will be farther from point A when they meet ?

You have four chains. Each chain has three links in it. Although it is difficult to cut the links, you wish to make a single loop with all 12 links. What is the fewest number of cuts you must make to accomplish this task?

What's the next in the series?

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