Maximum Size of First Member of a Period

There are several factors that influence the maximum size of the first member of a period in the periodic table. These include:

1. Maximum Number of Shells
The maximum number of shells that an element can have is directly related to its position in the periodic table. As we move from left to right across a period, the number of shells remains the same, but the size of the atoms decreases. This is because the increase in the number of protons in the nucleus attracts the electrons more strongly, making the atomic radius smaller.

2. Screening Effect
The screening effect is the ability of inner electrons to shield the outer electrons from the positive charge of the nucleus. As we move from left to right across a period, the number of protons in the nucleus increases, but the number of inner electrons remains the same. This results in a decrease in the screening effect, which makes the attraction between the nucleus and the outer electrons stronger, leading to a smaller atomic radius.

3. Minimum Effective Nuclear Charge (Zeff)
The effective nuclear charge is the net positive charge experienced by an electron in an atom. As we move from left to right across a period, the number of protons in the nucleus increases, but the number of inner electrons remains the same. This results in an increase in the effective nuclear charge, which makes the attraction between the nucleus and the outer electrons stronger, leading to a smaller atomic radius.

4. All Factors
All the factors mentioned above contribute to the maximum size of the first member of a period. The maximum size is determined by the balance between the attraction between the nucleus and the outer electrons and the repulsion between the electrons themselves. The number of shells, screening effect, and effective nuclear charge all play a role in this balance.

In conclusion, the maximum size of the first member of a period is determined by a combination of factors, including the maximum number of shells, screening effect, and effective nuclear charge. The balance between these factors determines the atomic radius of an element and its position in the periodic table.

Across a period the number of shells remains constant but the electrons enter in the same shell hence the effective nuclear charge increases thereby decreasing the atomic radii across a period, so the option is (3) minm effective nuclear charge therefore the size of first member of a period is max