A series of chemical elements is given with one term missing. Choose the correct alternative from the options that will complete the series. Hydrogen, Helium, Lithium, ?

Introduction / Context:
This question checks basic knowledge of the periodic table of elements, specifically the order of elements by increasing atomic number. The series Hydrogen, Helium, Lithium lists the first three elements. To find the missing fourth term, candidates must recall which element comes immediately after Lithium in the same sequence of atomic numbers. This is a straightforward recall based general science question often asked in competitive exams.

Given Data / Assumptions:

• Given series: Hydrogen, Helium, Lithium, ?
• Hydrogen has atomic number 1.
• Helium has atomic number 2.
• Lithium has atomic number 3.
• We assume the series lists elements in the order of increasing atomic number.

Concept / Approach:
In the periodic table, the elements are arranged according to increasing atomic number. After Lithium, which has atomic number 3, the next element is Beryllium with atomic number 4. The names Boron, Carbon, Nitrogen, and Oxygen follow later with atomic numbers 5, 6, 7, and 8 respectively. Therefore, to complete this simple atomic number series, we must choose the element that directly succeeds Lithium in the periodic table, which is Beryllium.

Step-by-Step Solution:
Step 1: List the first few elements of the periodic table in order of atomic number: Hydrogen (1), Helium (2), Lithium (3), Beryllium (4), Boron (5), Carbon (6), Nitrogen (7), Oxygen (8). Step 2: Compare this standard list with the given series: Hydrogen, Helium, Lithium, ? which clearly follows the same order so far. Step 3: Identify the element that comes immediately after Lithium (3) in the sequence. From the list, Beryllium with atomic number 4 is the next element. Step 4: Select Beryllium from the options as the correct term to complete the series.

Verification / Alternative check:
A quick verification is to recall the typical sequence taught in school: H, He, Li, Be, B, C, N, O. This exact order confirms that Beryllium always follows Lithium when elements are arranged by increasing atomic number. Since the series obviously uses this order, and Beryllium appears among the given options, our choice is fully consistent with the periodic table.

Why Other Options Are Wrong:
Boron has atomic number 5 and comes after Beryllium, so it is one step too far. Carbon, Nitrogen, and Oxygen have atomic numbers 6, 7, and 8, and appear even later in the period. None of these fits the requirement of being immediately after Lithium in the standard sequence, so they cannot be the missing fourth term in the series.

Common Pitfalls:
Some students may mistakenly remember the order as Hydrogen, Helium, Lithium, Boron and skip Beryllium, or confuse Beryllium with Boron due to similar sounding names. Another pitfall is to focus on chemical properties or group names instead of simply remembering the increasing atomic numbers. For quick factual series questions like this, memorising the first few elements in correct order is very helpful.

Final Answer:
The element that follows Lithium in the periodic table and completes the series is Beryllium.