There is no "why", because that's not what happens. The truth is
exactly the opposite.
Whatever the weight of a solid object is in air, that weight will appear
to be LESS when the object is immersed in water.
The object is lifted by a force equal to the weight of the fluid it displaces.
It displaces the same amount of air or water, and any amount of water
weighs more than the same amount of air. So the force that lifts the
object in water is greater than the force that lifts it in air, and the object
appears to weigh less in the water.
During the collision between two balls on the pool table there is no external force along the line of collision between them
Since there is no external force on it so here we can say

here we have

so we can say

since there is no external force so we can say during the collision the momentum of two balls will remain conserved
What gas? Gas is an invisible form so I don't see how it would have a "defined structure".
Can neither be created or destroyed.
Answer:
Answers at the bottom!!
Explanation:
For the first answer: Gamma ray
Gamma rays and x-rays consist of high-energy waves that can travel great distances at the speed of light and generally have a great ability to penetrate other materials. For that reason, gamma rays (such as from cobalt-60) are often used in medical applications to treat cancer and sterilize medical instruments.
For the second answer: They both have technological uses.
In my opinion I'm pretty sure it's A because we do use microwaves and x-rays as technological uses.
Hope this helps!!
Happy Holidays and Season Greeting!!
ii Feliz Navidad a todos !!