Which of the following period is the shortest one?

1

The correct answer is option (1) 1.

In the periodic table, periods are the rows running horizontally from left to right. Each period represents the energy levels (or shells) occupied by the electrons of the elements within that row. Here's an explanation of why Period 1 is the shortest period among the options provided:

1. Number of Elements:  Period 1 contains only two elements: hydrogen (H) and helium (He). These elements have electrons occupying the first energy level (also known as the K shell). Helium has its second energy level (the L shell) fully filled with electrons.

2. Energy Levels: Elements in Period 1 have their electrons confined to the first energy level. The first energy level can hold a maximum of 2 electrons. Since there are only two elements in Period 1, there are no elements with electrons in higher energy levels within this period.

3. Comparison with Other Periods:

• Period 2 contains eight elements, with electrons occupying both the first and second energy levels.
• Period 3 contains eight elements, with electrons occupying the first, second, and third energy levels.
• Period 4 contains 18 elements, with electrons occupying the first, second, third, and fourth energy levels.

4. Length of Periods: Since Period 1 has the fewest elements and the lowest number of energy levels occupied by electrons compared to the other periods, it is the shortest period in terms of the number of elements it contains.

In summary, Period 1 is the shortest period in the periodic table because it contains only two elements, hydrogen and helium, with electrons confined to the first energy level. This distinguishes it from the longer periods below it, which contain more elements and electrons occupying multiple energy levels.