What is the next number in this matchsticks series riddle?

I have lakes with no water, mountains with no stone and cities with no buildings. What am I?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

Can you Find and name the hidden bird in the picture below ?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

What does the following BrainBat signifies?

ABCDEFGHIJKLMNOPQRSTUVWYZ

QQQQQQQQQQQQQQQQQQQQQQQQQ.

Solve the mathematical equation in the picture below.

How many sides does a circle have?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

Can you find the thief by just looking at the picture below?