Solution:

Either Rain Cloud Or Air

Explanation
=== Rain Cloud ===
I don't have a mouth but can roar - Thunder
I don't have eyes but can cry - Rain
I am really good - Rain is good
but bad sometimes - Storms
Without me, all will die - rain is the necessity for agriculture and human being

=== Air ===
I don't have a mouth but can roar - Wind
I don't have eyes but can cry - Moisture
I am really good - Rain is good
but bad sometimes - Hurricanes
Without me, all will die - Oxygen

Solution:

They used the planks in the manner that is shown in the figure.

Solution:

Solution is shown in image below

Solution:

2003.

Explanation:
Its a series of prime numbes.

Solution:

74658

* 8 + 6 =14
* 5 - 4 = 1
* 7 = 2*4 - 1
* 4 + 6 = 10
* 7+4+6+5+8 = 30

Solution:

The two numbers are 4 and 13 whose product is 52 and sum is 17.

Solution:

There are three roses and four bees.

Solution:

The Winchester brothers - sam and dean

Solution:

The Stars

Solution:

The matchsticks that are marked with red are to be removed and the final figure will have just two squares. You can remove either pair from the possible four ways.

Solution:

Adam and Eve were the only people without navel. As they were not born out of a mother, they never had umbilical cords and thus never had navels.