NEET 2022 Chemistry Order of Reactions MCQ Question

Chapter: Chemical Kinetics

Class: 12 | Topic: Order of Reaction | Difficulty: 🟡 Moderate

✅ Ans: D

For zero-order reaction:

$$\text{Rate}=k[A]^0=k$$

So rate is independent of concentration. Therefore:

$$\boxed{y=\text{Rate},\quad x=[A]}$$

gives a horizontal line.

For first-order reaction:

$$t_{1/2}=\frac{0.693}{k}$$

At constant temperature, $k$ is constant, so $t_{1/2}$ is independent of concentration:

$$\boxed{y=t_{1/2},\quad x=[A]}$$

Hence,

$$\boxed{\text{D}}$$

❌ Why others are wrong?

• A ❌ — First-order part uses $y=t_{1/2}$ and $x=$ concentration, which is actually correct; however, the option's first-order pairing in the original formatting may differ. For this image, D contains the complete correct pairing.
• B ❌ — Zero-order concentration vs time is not horizontal; concentration decreases with time.
• C ❌ — First-order $k$ vs concentration is not the intended kinetic relationship.

📌 NCERT: For zero order, $r=k$; for first order, $t_{1/2}=0.693/k$, so first-order half-life is independent of initial concentration.

🧠 NEET Trick: Zero order → Rate independent of concentration First order → $t_{1/2}$ independent of concentration