Grouping Elements Based on Atomic Number

To determine which elements belong to the same group or sub-group, we need to analyze the given atomic numbers and look for patterns or similarities. Let's examine each option and identify the elements that belong to the same group or sub-group.

Option A: Atomic number = 12, 20, 4, 88
- Atomic number 4 corresponds to the element beryllium (Be).
- Atomic number 12 corresponds to the element magnesium (Mg).
- Atomic number 20 corresponds to the element calcium (Ca).
- Atomic number 88 corresponds to the element radium (Ra).

All of these elements belong to Group 2, also known as the alkaline earth metals. They have similar chemical properties, including a tendency to form 2+ cations and react with water to produce alkaline solutions.

Option B: Atomic number = 8, 16, 34, 2
- Atomic number 2 corresponds to the element helium (He).
- Atomic number 8 corresponds to the element oxygen (O).
- Atomic number 16 corresponds to the element sulfur (S).
- Atomic number 34 corresponds to the element selenium (Se).

These elements do not belong to the same group or sub-group. However, helium (He) belongs to Group 18, also known as the noble gases. Noble gases are characterized by their low reactivity and stable electron configurations.

Option C: Atomic number = 11, 18, 27, 5
- Atomic number 5 corresponds to the element boron (B).
- Atomic number 11 corresponds to the element sodium (Na).
- Atomic number 18 corresponds to the element argon (Ar).
- Atomic number 27 corresponds to the element cobalt (Co).

These elements do not belong to the same group or sub-group. However, sodium (Na) belongs to Group 1, also known as the alkali metals. Alkali metals are highly reactive and tend to form 1+ cations.

Option D: Atomic number = 24, 47, 42, 55
- Atomic number 24 corresponds to the element chromium (Cr).
- Atomic number 47 corresponds to the element silver (Ag).
- Atomic number 42 corresponds to the element molybdenum (Mo).
- Atomic number 55 corresponds to the element cesium (Cs).

These elements do not belong to the same group or sub-group. However, silver (Ag) belongs to Group 11, which also includes copper (Cu) and gold (Au). Group 11 elements are known as coinage metals.

Conclusion
From the given options, only Option A contains elements that belong to the same group or sub-group (Group 2 - alkaline earth metals). The other options do not have elements that share the same group or sub-group.

Option a :if u once see or recollect the periodic table once , u would understand it better