I am quite hot but become too cold if you remove the first two letters. What am I?

Quickly Solve this riddle

7 - 4 + 3 * 0 + 1 = ?

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

Christina, Allison and Lena are 3 daughters of John a well-known Mathematician, When I asked John the age of their daughters. He replied "The current age of her daughters is prime. Also, the difference between their ages is also prime."

How old are the daughters?

A man calls his dog from the opposite side of a river. The dog crosses the river without a bridge or a boat and manages to not get wet. How is this possible?

What am I?

Sherlock breaks into a crime scene. The victim is the owner who is slumped dead on a chair and have a bullet hole in his head. A gun lies on the floor and a cassette recorder is found on the table. On pressing the play button, Sherlock hears the message 'I have committed sins in my life and now I offer my soul to the great Lord' and followed a gunshot Sherlock smiles and informed the police that's its a murder.

Why did he think so?

How many letters are in the alphabet?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

Out of four images which one is the odd one out?