Answer: Option (C) is the correct answer.
Explanation:
An ion is defined as a specie which is formed when a neutral atoms tends to gain or lose an electron.
When a neutral atom gain an electron then it forms a negative ion whereas when a neutral atom tends to lose an electron then it forms a positive ion.
For example, a neutral fluorine atom on gaining an electron will form 
ion. And, a sodium atom on losing an electron forms 
ion.
When a group of atoms form ions then it tends to form polyatomic ions.
Thus, we can conclude that group of atoms that gains or loses electrons is called a polyatomic ion.
Answer:
B. Line 2 has a mistake
Explanation:
1. All electromagnetic waves are made of both electric and magnetic fields (hence the name electromagnetic).
2. All electromagnetic waves are transverse, and not longitudinal.
3. All electromagnetic waves can travel through space because they do not need particles to travel (like sound waves).
4. Electromagnetic waves all travel at the speed of light (299 792 458 m/s).
There can only be two electrons in the innermost shell of an atom so b is the correct answer
By adding acid to a basic solution of pH 12, the overall solution
becomes less basic and the Ph of solution decreases to a value of 7, which is
known as the pH of a neutral solution, i.e neither basic nor acidic. This process
is called neutralizing the base.
