What is common among 11, 69, and 88?

Rebus Puzzle Definition: A rebus is an illusion device that uses pictures to represent words or parts of words.
What does This Rebus Puzzle Identify?

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

A seven-year-old kid challenged his classmates that he can make the number one disappear by adding something to it.

How can he do that?

How can you write nineteen in a manner that if we take out one, it becomes twenty?

In the Thar desert, 3 men found a big 24L Jar is full of water. Since there is a shortage of water so they decided to distribute the water among themselves such that they all have equal amounts of it. But they only have a 13L, a 5L and an 11-litre Jar.

How do they do it?

Take number 1000 and then add 20 to it.
Now add 1000 one more time.
Now add 30.
Now add 1000 one more time.
Now add 40.
Now add 1000 one more time.
Now add 10.

What is the total?

What does this mean?

CCCCCCC

With the help clues provided in the image, can you find the 5 digit key?

The person who makes it has no need for it. He who purchases it does not use it. The person who does use it does not know they are. What is it?