Which number should replace the question mark?

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

I don't get anymore wetter, no matter how much rain falls on me.

An express train takes 3 seconds to enter the tunnel which is 1 km long.
If it is travelling at 120 km an hour, how long will it take to pass completely through the tunnel?

You have 1023 apples and 10 bags. You have to distribute these apples in these 10 bags in any way you choose. But when I ask for a certain number of apples you have to give them in terms of bags without transferring the apples from other bags. How do you distribute the apples?

Can you make a six-letter word using the letters N, A and B ?

Can you find the odd number in the following?

2716, 4135, 5321 and 7145

How many times do a clock's hands overlap in a day ?

Which is Odd One Out and why?

4377

3954

9862

8454

9831

I am a type of room you cannot enter or leave. Raised from the ground below, I could be poisonous or a delicious treat. What am I?