Answer:
1. Isotopes are atoms of an element that consist of the same number of protons but a different number of neutrons.
2. No. of protons = 13
No. of neutrons = 27 - 13
= 14
3. refer to attached file
4(a). Since the noble gases can be found in group 18 of the periodic table, it suggests that they have a complete octet (a full valence shell of electrons), and this allows them to be stable gases that show the least reactivity.
4(b). Since the number of protons and electrons are equal in an atom, the opposite charges are balanced and thus, there is no net charge on the atom (neutrons present in the atom have no charge). Hence, an atom is electrically neutral.
5. Mass no. of X = 6 + 6
= 12
Mass no. of Y = 6 + 8
= 14
6. mass number = no. of protons in the nucleus of an atom + no. of neutrons in the nucleus of an atom
atomic number = no. of protons in the nucleus of an atom
isobars = atoms of elements which have the same mass number but different atomic numbers
isotopes = atoms of elements which have the same number of protons but a different number of neutrons