Introduction:
In atomic physics, the electron shells are energy levels or regions where electrons are likely to be found around an atomic nucleus. These shells are labeled using letters: K, L, M, N, O, P, Q, with K being the closest to the nucleus. Each shell can hold a specific number of electrons.

Explanation:
To determine which shell would be the first to have a g subshell, we need to understand the order in which the subshells are filled according to the Aufbau principle and the periodic table.

Aufbau Principle:
The Aufbau principle states that electrons fill the lowest energy levels first before occupying higher energy levels. The order of filling the subshells is as follows:

1. s subshell
2. p subshell
3. d subshell
4. f subshell
5. g subshell (if it exists)

Periodic Table:
The periodic table is organized based on the electronic configuration of elements. It provides a systematic arrangement of elements according to their atomic number (number of protons in the nucleus). The rows in the periodic table are called periods, and the columns are called groups.

Identifying the First Shell with g Subshell:
1. The first shell is the K shell, which consists of only an s subshell (1s). It can hold a maximum of 2 electrons.
2. The second shell is the L shell, which includes both s and p subshells (2s and 2p). It can hold a maximum of 8 electrons.
3. The third shell is the M shell, which includes the s, p, and d subshells (3s, 3p, and 3d). It can hold a maximum of 18 electrons.
4. The fourth shell is the N shell, which includes the s, p, d, and f subshells (4s, 4p, 4d, and 4f). It can hold a maximum of 32 electrons.
5. The fifth shell is the O shell, which includes the s, p, d, f, and g subshells (5s, 5p, 5d, 5f, and 5g). It can hold a maximum of 50 electrons.

Based on the above information, the first shell to have a g subshell is the O shell (5s, 5p, 5d, 5f, and 5g), which is option (4).

Conclusion:
The first shell to have a g subshell is the O shell, as it includes the s, p, d, f, and g subshells. The other options, L (1), M (2), and N (3), do not have the g subshell.

O shell