Question:

\(P \rightarrow Q\) is a zero order reaction. If the concentration of \(P\) decreases from \(0.1\ M\) to \(0.05\ M\) in 10 seconds, then the concentration of \(P\) after 15 seconds is

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For a zero order reaction, \[ [A]_t=[A]_0-kt \] The concentration decreases linearly with time, and the rate is independent of concentration.
Updated On: Jun 18, 2026
  • \(0.05\ M\)
  • \(0.025\ M\)
  • \(0.02\ M\)
  • \(0.01\ M\)
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The Correct Option is B

Solution and Explanation

Step 1: Use the integrated rate equation for a zero order reaction.
For a zero order reaction, \[ [P]_t=[P]_0-kt \] where \[ [P]_0=\text{initial concentration} \] and \[ [P]_t=\text{concentration after time } t \]

Step 2: Calculate the rate constant.

Given, \[ [P]_0=0.10\ M \] and after \(10\ s\), \[ [P]_{10}=0.05\ M \] Using \[ [P]_{10}=[P]_0-k(10) \] \[ 0.05=0.10-10k \] \[ 10k=0.05 \] \[ k=0.005\ M\,s^{-1} \]

Step 3: Calculate the concentration after 15 seconds.

Using \[ [P]_{15}=0.10-(0.005)(15) \] \[ =0.10-0.075 \] \[ =0.025\ M \]

Step 4: Final conclusion.

Therefore, the concentration of \(P\) after \(15\ s\) is \[ \boxed{0.025\ M} \] Hence, the correct option is (2).
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