What does this rebus mean?

O
N
C
E
TIME

Why is the Hole below a Lock?

By including only four matchsticks in below picture, you have to make "Four Triangles And Two Squares"

When we see 2 but call 10?

Find three numbers such that When we multiply three numbers, we will get the prime numbers. The difference between the second and the first number is equal to the third and second.

What has many teeth, but cannot bite?

What does below science rebus mean?

Ag Ag Ag
Ag SPOON Ag
Ag Ag Ag

I have branches, but no fruit, trunk or leaves. What am I?

I am not alive, but I grow; I don't have lungs, but I need air; I don't have a mouth, but water kills me. What am I?

You walk into an old horror house. It has no power or plumbing. Once inside, you see three doors. Each door has a number on it. Behind each door is a way for you to die. Behind door number one, you die by getting eaten by a lion. Behind door number two, you die by getting murdered. Behind door number three, you die by an electric chair. You can’t turn back, so you have to go through a door. Which door do you go through?