The mass number is given as 40. So the nucleus’ relative mass must also be 40. Therefore, 1 is incorrect.
Noble gases have full outer shells. This element has an atomic number of 20.
So the electronic configuration of this element is 2,8,8,2. This element does not have a full outer shell. So 2 is incorrect.
This element has 2 electrons on its outer shell. So, it will lose 2 electrons to become stable forming a positive ion. It will not form a negative ion. So 3 is not correct.
This element has 2 electrons on its outer shell. The number of electrons in an element’s outer shell determines which group it belongs to. So this element is in group 2. Hence, 4 is correct.
Since it is in group 2, it must be a metal. 5 is not correct.