9701 MCQ Solution 2

Question 2: [Physical > Atomic Structure]

One of the most important chemical species responsible for the removal of ozone from the stratosphere is a free radical of chlorine, ³⁵Cl • .

What does ³⁵Cl • contain?

	protons	neutrons	electrons
A	17	18	16
B	17	18	17
C	18	17	17
D	18	17	18

Reference: Past Exam Paper – November 2002 Paper 1 Q2

Solution 2:

Answer: B.

Using the data booklet we find that for a particle to be described as chlorine it needs to have 17 protons. 35 is the given mass number of the free radical thus 35 – 17 = 18. There are 18 neutrons because protons and neutrons are the only particles in an atom that carry mass. The free radical does not carry a charge thus meaning that opposing charge carrying particles (protons and electrons) must be equal in number so they cancel out to give no overall charge.