Can you place six X (crosses) in below board without making three in a row in any way ?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

The centre of the third figure is empty. What digit should fit inside?

To attend world science seminar, A famous chemist from Mexico visit
London. In the lab, the scientist was killed and his six assistants were under suspicion of killing the chemist.
Name of six assistants: Austin, Wayne, Dege, Oscaru, Lingard, and Rojo.
He left a note "76-20-44 79-16-22-7"

A local detective Jack was called to solve the case,

After reading the note, Jack instantly asked the police to arrest the murderers.

Who are the murderers?

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

Which of the below owl is odd one out?

Which word is least like the others? Third, fourth, fifth, sixth, seventh, eighth, ninth?

A beggar on the street can make one cigarette out of every 6 cigarette butts he finds. After one whole day of searching and checking public ashtrays the beggar finds a total of 72 cigarette butts. How many cigarettes can he make and smoke from the butts he found?

John has eleven friends. He has a bowl containing eleven apples. Now He wants to divide the eleven apples among his friends, in such a way that an apple should remain in his bowl.
How can He do it?

People make me, save me, change me, raise me. What am I?