Question

Assertion :${\left[Al{\left(H_{2}O\right)}_6\right]}^{3+}$ is stronger acid than ${\left[Mg{\left(H_{2}O\right)}_6\right]}^{2+}$. Reason: ${\left[Al{\left(H_{2}O\right)}_6\right]}^{3+}$ possess more effective nuclear charge due to smaller size of ${\left[Al{\left(H_{2}O\right)}_6\right]}^{3+}$.

Choose the correct option.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

Given hydrated complex

$\left[Al\right(H_{2}O{)}_6{]}^{3+}$ and $\left[Mg\right(H_{2}O{)}_6{]}^{2+}$

$A{l}^{3+}\Rightarrow 1s^{2}2s^{2}2p^6$ (No. of protons $=13$)

$M{g}^{2+}\Rightarrow 1s^{2}2s^{2}2p^6$ (No. of protons $=12$)

The acidic strength of given complex depend on how strongly these pulls electrons.

As we know that more will be the +ve charge more will be attracting power to pulls electrons.

Therefore,

$\left[Al\right(H_{2}O{)}_6{]}^{3+}>\left[Mg\right(H_{2}O{)}_6{]}^{2+}$

Electronegativity $\uparrow \Rightarrow$ Effective nuclear charge

$\Downarrow$

Attraction of electron $\uparrow \Rightarrow$ Acidic strength $\uparrow$