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.
Answer:

Explanation:
As we know that the displacement of the particle from the mean position is 1/5 times of its amplitude
so we have


so now we have

now we have

so the phase other particle in opposite direction is given as

so we have phase difference given as


Answer:
A. It is colder at the top of a mountain
Explanation:
The answer would be:
B. Chlorine, iodine and Fluorine
Barium has 2 valence electrons. To satisfy the BaX₂ , this would mean that Barium will need to give one of each of its electrons. The elements that need 1 electron would be those that have 7 valence electrons to complete the octet. These elements would fall in group 7 or halogens. Chlorine, iodine and fluorine are all in Group 7, so this would be the best choice.
Electromagnet is in form of solenoid
and the magnetic field due to solenoid is given as

here
i = current in the loop
so when we increase the current in electromagnet the magnetic field of the solenoid will increase
this will increase the strength of the electromagnet
so the answer would be
<em>INCREASE</em>