JEE Chemistry 2024 Question with Solution

Given: Two statements about periodic trends and the nature of oxides are to be evaluated.

Find: Which option correctly identifies the truth values of Statement I and Statement II.

Statement I says that chemical reactivity gradually increases across a period from group $1$ to group $18$. This is incorrect because chemical reactivity does not follow one uniform increasing trend across a period.

For metals on the left side of the periodic table, reactivity generally decreases across a period because ionization energy increases and loss of electrons becomes more difficult.

For non-metals on the right side, reactivity generally increases due to increasing electronegativity and electron affinity. However, group $18$ elements are largely inert.

Therefore, Statement I is false.

Statement II says that oxides formed by group $1$ elements are basic, while those of group $17$ elements are acidic. This is correct.

Group $1$ elements form basic oxides such as $\mathrm{Na_2O}$ and $\mathrm{K_2O}$, which react with water to form bases like $\mathrm{NaOH}$.

Group $17$ elements form acidic oxides such as $\mathrm{Cl_2O_7}$, which react with water to form acids like $\mathrm{HClO_4}$.

Therefore, Statement II is true.

Hence, Statement I is false while Statement II is true. The correct option is C.

Given:

• Statement I concerns the trend of chemical reactivity across a period.
• Statement II concerns the acidic or basic nature of oxides of group $1$ and group $17$ elements.

Find: The correct combination of truth values.

Step 1: Evaluate Statement I.

Chemical reactivity across a period is not monotonic. Metals at the left of the periodic table are highly reactive because they lose electrons easily. As we move across the period, ionization energy increases, so metallic reactivity decreases.

Non-metals toward the right side tend to gain electrons more readily, so their reactivity increases in a different sense. But noble gases in group $18$ are mostly inert.

So there is no gradual increase in reactivity from group $1$ to group $18$.

Thus, Statement I is false.

Step 2: Evaluate Statement II.

Group $1$ elements are alkali metals and form basic oxides. Examples include $\mathrm{Na_2O}$ and $\mathrm{K_2O}$.

Group $17$ elements are halogens and their oxides are acidic in nature. An example is $\mathrm{Cl_2O_7}$, which forms an acid on reaction with water.

Thus, Statement II is true.

Conclusion: Statement I is false and Statement II is true. Therefore, the correct option is C.