What does below chemistry rebus means?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

Before the start of the car race, John and Jacob have the same amount of fuel in their car. With this fuel, John can drive for 4 hours while Jacob can drive five hours.
After a time they realize that the amount of fuel left in John's car is 1/4th of the fuel in Jacob's.

For how long they are racing?

A gardener planted the Lemon trees in a mathematical ordered way (i.e. he planted a tree in rows).
He created a total of 19 rows of trees.

Note: There should be more than 2 trees to count as a row.

What is the minimum number of trees required by the gardener to have 19 rows of trees?

Christina is practising her dance steps along with her friends. In a particular sequence, all of them form a row. At that point, Niharika is standing in the 4th position from either end of the row.
Can you find out how many girls are practising together?

You’re out on the water and see a boat filled with people. You look away for a second and look back again, but this time you don’t see a single person on the boat. Why? Hint: The boat did not sink.

Considering the below equation:

V + II - VI = 10
IV - X + VIII = 20
IV - VII + VI = 30

Then, I + II + III = ?

You have to fill the below given grid in a manner that every row and column contains the digits 1 to 6. Also, make sure that the squares that are connected with each other must contains the same digit.

What month of the year has 28 days?

John was born on March 5, 1970, in Delhi, India. Jacob was born 25 days before John. The year when they took birth, Republic Day fell on Monday.

Can you find out on what day was Jacob born?