What does below chemistry rebus means?

You see a boat filled with people, yet there isn’t a single person on board. How is that possible?

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

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

The first box has two white balls. The second box has two black balls. The third box has a white and a black ball.

Boxes are labeled but all labels are wrong!

You are allowed to open one box, pick one ball at random, see its colour and put it back into the box, without seeing the colour of the other ball.

How many such operations are necessary to correctly label the boxes?

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?

Can you count the number of lines in the below picture?

Which is heavier: a ton of bricks or a ton of feathers?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

Cristina leaves home and then she makes exactly 3 left turns and returns home where she found 2 girls wearing the mask.

Who are these two masked girls?

Two in a corner, one in a room, zero in a house, but one in a shelter. What am I?