Answer: electron donor.
Explanation:
According to Arrhenius concept, a base is defined as a substance which donates hydroxide ions 
when dissolved in water and an acid is defined as a substance which donates hydronium ions 
in water.
According to the Bronsted Lowry conjugate acid-base theory, an acid is defined as a substance which donates protons and a base is defined as a substance which accepts protons.
According to the Lewis concept, an acid is defined as a substance that accepts electron pairs and base is defined as a substance which donates electron pairs.
Here 
acts as lewis base and 
act as lewis acid.
Thus lewis base is defined as an electron pair donor.
Mg (s) + HCl (aq) → MgCl₂(s) + H₂(g)
Looking at the equation :
We have 1 Mg at the left hand side and 1 Mg as well on the right hand side.
So that is balanced.
We have 1 H at the left hand side and 2 H on the right hand side.
So that is not balanced. Same for Chlorine. Cl.
We add 2 to the HCl on the left hand side and that balances it.
Mg(s) + 2HCl(aq) → MgCl₂(s) + H₂(g)
Answer:
radio waves
Explanation:
On the far left of the diagram are radio waves, which include microwaves. They have the longest wavelengths and lowest frequencies of all electromagnetic waves. They also have the least amount of energy.
