Answer:
element S is argon and element T is potassium.
4. B
5. D
Step-by-step explanation:
in an element in periodic table number of elctrons and protons are same.
4. since element S has 18 protons so its atomic number must be 18 so the element is Argon which is the last element of period 4 so the next element will go to period 4 with one extra shell and since the atomic number of next element is 19 the element is Potassium. therefore T is Potassium.
5. number of nucleons in an atom is the number of protons and neutons combined together in an nucleus