What does below chemistry rebus means?

If 21x = 79x, what is the value of x?

What word begins and ends with an E, but has only one letter?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

Name the three-letter word that can complete the below words:

A) L O _ _ _ E
B) E D U _ _ _ E
C) _ _ _ E R
D) _ _ _ T L E

It has horns but can’t beep. It is like to bleat but It is not a sheep. What is it?

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

Can you find the ages of a son, father and grandfather based on the following facts?
The sum of the ages of grandfather, father and son is 140 years.
The age of the son in months is the same as the grandfather in years.
The age of the son in days is the same as the father in weeks.

Replace all '*' with digits 1, 2, 3, 4, 5 and 6 to make below statement true.

* *
x *
=====
* * *

What can run but never walk, have a mouth that never speaks, have a head that never weeps, and have a bed but never sleeps?