MHT CET · Chemistry · Classification of Elements and Periodicity in Properties

Which of the following elements belongs to first group and fifth period of periodic table?

A Rubidium
B Strontium
C Caesium
D Barium

Verified Solution

Answer & Solution

Correct Answer

(A) Rubidium

Step-by-step Solution

Detailed explanation

(1) Rubidium (Rb): Rubidium is in Group 1 (alkali metal) and Period 5. This is a correct match.
(2) Strontium (Sr): Strontium is in Group 2 (alkaline earth metals), not Group 1.
(3) Caesium (Cs): Caesium is in Group 1, but it is in Period 6, not Period 5.
(4) Barium (Ba): Barium is in Group 2 (alkaline earth metals), not Group 1.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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