Chemistry Q135 – AP-EAMCET 2026

Home Chemistry Periodicity & ElementsQuestion #493

Observe the following statements about the oxides of group 14 elements I.

C O_{2}

is an acidic oxide but

C O

is a neutral oxide II. Cristobalite is the crystalline form of silica III. Liquid

C O

is called dry ice IV. Both

C O

and

C O_{2}

act as Lewis acids The correct statements are

Clue 1 of 3: Properties of Oxides

Recall the general classification of oxides (acidic, basic, neutral, amphoteric) based on the nature of the element and their reactions with acids and bases.

🧠 Full Solution Path

Step 1: Evaluate Statement I: Acidic/Neutral Nature of Carbon Oxides✦ Active

Statement I claims that $C O_{2}$ is an acidic oxide and $C O$ is a neutral oxide. Carbon dioxide ( $C O_{2}$ ) reacts with water to form carbonic acid ( $H_{2} C O_{3}$ ), and it reacts with bases, confirming its acidic nature. Carbon monoxide ( $C O$ ) is known to be a neutral oxide, meaning it does not react with acids or bases. Therefore, Statement I is correct.

💡 Teacher's Secret Hint

Acidic oxides are typically formed by non-metals and react with bases or water to form acids. Neutral oxides do not react with acids or bases.

Step 2: Evaluate Statement II: Crystalline Form of Silica○ Expand

Statement II states that Cristobalite is a crystalline form of silica. Silica ( $S i O_{2}$ ) exists in several crystalline forms (polymorphs), including quartz, tridymite, and cristobalite. Cristobalite is indeed one of the high-temperature forms of silica. Therefore, Statement II is correct.

💡 Teacher's Secret Hint

Remember that many compounds can exist in different structural forms, known as allotropes or polymorphs, each with distinct properties.

Step 3: Evaluate Statement III: Definition of Dry Ice○ Expand

Statement III claims that liquid $C O$ is called dry ice. Dry ice is the common name for solid carbon dioxide ( $C O_{2}$ ), which sublimes directly from solid to gas at room temperature and pressure. Liquid carbon monoxide ( $C O$ ) is just liquid $C O$ , not dry ice. Therefore, Statement III is incorrect.

💡 Teacher's Secret Hint

Confusion between $C O$ and $C O_{2}$ is common. Always double-check the chemical formula for common substances.

Step 4: Evaluate Statement IV: Lewis Acid Behavior of Carbon Oxides○ Expand

Statement IV asserts that both $C O$ and $C O_{2}$ act as Lewis acids. A Lewis acid is an electron-pair acceptor. In $C O_{2}$ , the central carbon atom is electron-deficient and can accept electron pairs, for example, from hydroxide ions ( $O H^{-}$ ), thus acting as a Lewis acid. Carbon monoxide ( $C O$ ), however, typically acts as a Lewis base (electron-pair donor) through the lone pair on its carbon atom, especially in coordination chemistry to form metal carbonyls. While it can accept electron density into its antibonding orbitals (acting as a $π$ -acceptor ligand), it is not generally classified as a Lewis acid in the typical sense of forming a bond by accepting a lone pair from a Lewis base. Therefore, the statement that *both* act as Lewis acids is incorrect because $C O$ is primarily a Lewis base. Statement IV is incorrect.

💡 Teacher's Secret Hint

Recall that a Lewis acid accepts an electron pair to form a new bond, while a Lewis base donates an electron pair. Carbon monoxide is a classic example of a neutral Lewis base ligand.

Step 5: Conclusion○ Expand

Based on the evaluation: Statement I: Correct Statement II: Correct Statement III: Incorrect Statement IV: Incorrect The correct statements are I and II only. This corresponds to option 1.

💡 Teacher's Secret Hint

Always review all options and statements thoroughly before making a final selection.

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Chemistry Question 135 – AP-EAMCET 2026

Clue 1 of 3: Properties of Oxides

🧠 Full Solution Path