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

In a university, a professor gave a set of three problems to the three brilliant students of his class. See the image for the questions.

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?

There were two grandmothers and their two granddaughters.
There were two husbands and their two wives.
There were two fathers and their two daughters.
There were two mothers and their two sons.
There were two maidens and their two mothers.
There were two sisters and their two brothers.
Yet there are only six, who are buried here,
All are born legitimate and relationships clear.
How can this happen?

Decode below three cipher riddles:

26 L of the A
7 D of the W
1000 Y in a M

You throw me out when you want to use me and you take me in when you don't want to use me.

Who Am I?

What is so fragile that saying its name breaks it?

In the given figure, you can see that four match sticks are used to form a square. Can you form five squares by using six matches?

Once while in his court, King Akbar asked Birbal to write something on a wall that makes one sad when read in good times and makes one happy when read in sad times.

He took only a few moment and wrote something that fit the requirements. What did he write?

The world's largest Thanksgiving turkey was on display at a fair. Everyone was admiring it when suddenly a woman ran up and shot the turkey and left. Everyone knew her yet nobody made any attempts to stop or report her. Why?