What does below chemistry rebus means?

Can you find the missing letter in the sequence?
S - T - I - L - ? - T - F - Y - C

A girl is twice as old as her brother and half as old as her father. In 50 years, her brother will be half as old as his father. How old is the daughter now?

John's five friends Rachel, Jacob, Phoebe, Joey and Chandler live on the same road.

Rachel lives in the house: A, Jacob lives in the house: B, Phoebe lives in the house: C, Joey lives in the house:D, Chandler lives in the house: E

Mathematically
B*C*D = 1260
B + C + D = 2E
2A = E

The road numbers run from 2 to 222.

Can you tell me the house number of each of John's friends?

John was so frustrated to be the suspect of being a sleeper terrorist that he shoot himself right between the eyes with a revolver in his toilet. The revolver and the bullets were accurate. Minutes later John walks out of the toilet unharmed.
How can this be possible?

A father's child, a mother's child, yet no one's son.

Who am I?

If,

Akriti = 631
Levis = 521
Sroti = 521
Aneel = 533
Then,
Sunil =?

John killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?

Quickly Solve this riddle

7 - 4 + 3 * 0 + 1 = ?

When monkey rotate the gear, which mark will be hit 1 or 2 ?