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(A): The atomic size of gallium is less ...

(A): The atomic size of gallium is less than expected
(R): In gallium the `3^(10)` delectrons do not shield effectively

A

A and R are true, R explains A

B

A and R are true, R does not explain A

C

A is true, but R is false

D

A is false, but R is true

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question regarding the assertion and reason about gallium's atomic size, we can break it down into several steps: ### Step-by-Step Solution: 1. **Understanding the Assertion**: - The assertion states that "the atomic size of gallium is less than expected." - This implies that gallium's atomic radius is smaller than what would typically be predicted based on its position in the periodic table. 2. **Understanding the Reason**: - The reason provided is that "in gallium, the 3d10 electrons do not shield effectively." - This suggests that the electrons in the 3d subshell do not provide adequate shielding for the outermost electrons from the nucleus's positive charge. 3. **Analyzing the Shielding Effect**: - Shielding occurs when inner electrons reduce the effective nuclear charge felt by the outer electrons. - In gallium, the presence of the 3d10 electrons means that these electrons are not effectively shielding the valence electrons (4s and 4p) from the nucleus. 4. **Implications of Poor Shielding**: - Due to the poor shielding effect of the 3d10 electrons, the outermost electrons experience a stronger attraction from the nucleus. - This increased nuclear attraction pulls the outermost electrons closer to the nucleus, resulting in a smaller atomic radius than expected. 5. **Conclusion**: - Both the assertion and the reason are true. The reason provided accurately explains why gallium's atomic size is less than expected due to the ineffective shielding by the 3d10 electrons. 6. **Final Answer**: - Therefore, the correct conclusion is that both the assertion (A) and the reason (R) are true, and R explains A.
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