GCSE / O Levels Chemistry

The diagram shows the outer shell electrons of the atoms of two elements, Q and R.
key
x = an electron
} = a nucleus
A
B
с
D
proton
number of Q
The sulfate of Q is insoluble.
Element R is gaseous at room temperature and pressure.
Which row could be correct?
12
12
56
56
R
20
35.5
80
80
35.5
relative atomic
mass of R
**

Choice D is correct because: 

Since Q has only 2 electrons in its valence shell, it can be deduced that Q is a metal.

As Q forms an insoluble sulfate, it can be concluded that Q is Barium.

Barium sulfhate is insoluble and barium has a proton number of 56.

Since R has 7 valence electrons, it can be deduced deduce that R is a non-metal.

As R is gaseous at room temperature and pressure, it can be concluded that R is chlorine.

Chlorine is a greenish yellow gas at room temperature and atmospheric pressure and has an atomic mass of 35.5.

Choices A, B and C are incorrect because they do not correctly identify the proton number of Q and the atomic mass of R.

Atomic Structure | 2022 - O/N - 5070/11 | Q5