The approximate composition of Portland cement is

Explanation:

The typical composition of Portland cement includes the following major compounds:

1. Tricalcium Silicate (C₃S): About 45-60% – Responsible for the early strength and hardening of the cement. It hydrates quickly and contributes significantly to the initial setting time and early strength gain.

2. Dicalcium Silicate (C₂S): About 15-30% – Reacts more slowly than C₃S and contributes to the strength of the cement over a longer period, providing long-term strength and durability.

3. Tricalcium Aluminate (C₃A): About 8-12% – Reacts quickly with water, generating a significant amount of heat, which is why it is controlled in cement to reduce heat of hydration and prevent quick setting. It also affects sulfate resistance.

4. Tetracalcium Aluminoferrite (C₄AF): About 6-10% – Provides the grey color to the cement and has a minor role in the hydration process.

5. Other Bonding Agents: These usually include gypsum (about 3-5%) to control the setting time and minor impurities.

Option 4 matches the approximate composition of Portland cement most closely, making it the correct choice. Other options either have incorrect proportions or unlikely combinations that do not reflect the typical composition of standard Portland cement.