The position of three elements A, B, and C in the Periodic Table are shown below: Group 16, Group 17 - A - B C
(a) State whether A is a metal or non-metal.
(b) State whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size than B?

(a) A belongs to group 17. There are 7 electrons in its valence shell. Therefore, it tends to accept one electron to complete its octet. Hence, it is a non-metal.
(b) C is less reactive than A. As both elements belong to the same group and going down the group, the size of the element increases. A is smaller than C; therefore, the cloud of electron density surrounding the nucleus is more compact. The stability of completing the octet for A is greater than for C as A is more keen to obtain an electron than C.
(c) C is smaller than B. C and B belong to the same period. Atomic radius decreases from left to right within a period. This is caused by the increase in the number of protons and electrons across a period. One proton has a greater effect than one electron; thus, electrons are pulled towards the nucleus, resulting in a smaller radius.
(d) A will form an anion A⁻. A belongs to group 17. There are 7 electrons in its valence shell. Therefore, it tends to accept one electron to complete its octet and forms an anion.