What does this rebus mean?

O
N
C
E
TIME

Can you solve the rebus below?

When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

You have two rectangular wires.

Both of them have property that when you light the fire from one end , it will take 60 minutes to get completely burn.

However, they do not burn at consistent speed (i.e it might be possible 1st 20% burn in 50 minutes and 80% can burn in 10 minutes).

So how could you measure 45 minutes ?

No one wants to have it, but if one got it, he does not want to lose it. What is It?

Begin with a word, five letters to my name,
Remove the first and last but I am the same
Take out my middle and still, I remain.
What word am I?

You are confined in a room and given two metal rods. Out of these two rods, one is magnet and the other is the iron rod. They look starkly similar. You don't have any other metal object in the room.

How will you decide which one of those is magnet?

By moving just one matchstick, you need to make the below statement true. Can you do it?

An exterior architect is asked by a builder to plant seven trees in a manner that there are exactly six rows of trees in a straight line and each row has three trees in particular.

How will he do it?

What is next number in the pattern below:

131 517 192 123 ?