1.14 deduce the electronic configurations of the first 20 elements from their positions in the periodic table

The arrangement of electrons into shells for an atom is known as its 'electronic configuration'.

The first row pf the periodic table has 2 electrons in its complete shell, all of the others have 8 (as far as GCSE is aware).They are given in shorthand notations, e.g.
Carbon is on the second row and has 6 electrons altogether (4 on its outer shell, 2 on its first shell) so its electron configuration would be 2.4
Magnesium is on the third row, has 12 electrons altogether (2 on its first shell, 8 on its second and 2 on its outer), so its electron configuration would be 2.8.2

As we are given a periodic table in the exam, we don't have to remember all of the electron configurations for the first 20 elements, we just be able to state them if asked.