What does below chemistry rebus means?

What does below rebus means ?

what's the probability of getting a king or a queen from a pack of 52 cards?

What part of the chicken has the most feathers?

What will be the best approach to finding all the prime numbers less than 75 that leave an odd reminder when we divide them with 5?

In four steps you need to move the word 'cold' From 'warm' by replacing one alphabet at a time such that every word formed at each step is acceptable in English Dictionary.

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

I get hot but I never sweat,
I cook food but I am not a chef,
I have a door but you can't enter me,
I have a light but I am not a lamp.
Who am I?

Two friends were betting. One said to the other, "The coin will be flipped twenty times and each time the coin lands on the head, I will give you $2 and each time it lands on the tale, you will give me $3." After flipping the coin twenty times not a single penny was exchanged among them.

How many times did the coin land on heads?

Can you count the number of triangles in the given picture?