According to Mendeleev, the properties of elements are the periodic functions of their atomic masses.

A group is determined by the number of electrons present in outermost shell.

Carbon is the representative element of group 14.

The elements in group 17 are called as halogens because they all form salts.

Fluorine is an element of halogen group.

Sulphur is a member of oxygen family, which is of group 16. Its oxides are acidic in nature.

The number of shells in an atom determines its period in periodic table. If an element has one shell, it is kept in first period and so on.

It is the electronic configuration of bromine.

The valency of an atom is equal to the number of electrons, which an atom can donate, accept or share to attain the configuraton of inert elements.

The atomic radius of fluorine atom is 64 pico metre. It is clear that fluorine is the smallest atom among the given options.

Greater the tendency to lose electrons, stronger is the reducing agent. Here the atom of sodium has the maximum metallic character. So, it is the strongest reducing agent.

$Cl^-$ is an anion. Hence, it is larger than its parent atom Cl.

Inert gases have zero electron affinity. Therefore, helium is an inert gas.

Sodium is a member of group I and period 3. Hence, it is correctly matched.

The periodic table by Mendeleev could not explain the position of isotopes. It is because it is based upon the atomic masses of elements.