Element X has the electronic structure 2, 8, 3.
Which of the following statements about this element are correct?
1 The element is in Group 12, Period 3 of the Periodic Table.
2 The element reacts with oxygen to form a compound with the formula X2 O3.
3 The element reacts with bromine to form a compound with the formula XBr 3.
4 The atomic number of the element is 13.
5 The element is an alkali metal.

Answer:

2) F

1 – there is no element in group 12 and period 3

2 – X has 3 electron in its outermost shell and so has a valency of +3. Oxygen has 6 electron in its outermost shell. It can accept 2 electrons and so, it has a valency of -2. If X reacts with Oxygen, the formula would be X2O3.

3 – Valency of X = +3. Valency of Br = -1. Formula would be XBr3 

4 – The atomic number is the number of protons in an atom. The number of electrons in an atom is equal to the number of protons. No. of electrons = 2+8+3 = 13. Hence, no. of protons = 13

5 – Alkali metals are only in group 1. X has 3 electron in its outermost shell. Hence, X is in group 3. 

The number of outermost electrons help to determine which group the atom is in.