---
title: "A student studies the photobleaching of an aqueous pigment, \\(\\text{P}\\), under constant illumination. The student measures \\([\\text{P}]\\) at several times and constructs the graph shown.  Which of the following statements about the reaction order is best supported by the graph?"
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url: "https://nerd-notes.com/ubq/119382/"
date_modified: "2026-08-19T12:40:05+00:00"
---

# A student studies the photobleaching of an aqueous pigment, \(\text{P}\), under constant illumination. The student measures \([\text{P}]\) at several times and constructs the graph shown.

Which of the following statements about the reaction order is best supported by the graph?

A student studies the photobleaching of an aqueous pigment, \(\text{P}\), under constant illumination. The student measures \([\text{P}]\) at several times and constructs the graph shown.

Which of the following statements about the reaction order is best supported by the graph?

![Draw a grayscale Cartesian graph with no gridlines. Label the horizontal axis “Time (min)” and mark 0, 10, 20, 30, and 40 at evenly spaced positions. Label the vertical axis “\([\text{P}]\) (M)” and mark 0.00, 0.20, 0.40, 0.60, and 0.80 at evenly spaced positions. Plot exactly five solid black circular data markers at (0, 0.80), (10, 0.60), (20, 0.40), (30, 0.20), and (40, 0.00). Draw one thin solid best-fit line passing through all five markers, descending from the upper left to the lower right. Use linear scales beginning at the origin, with arrowheads only at the positive ends of both axes. Do not include a legend, equation, slope triangle, uncertainty bars, extrapolation, or any additional curves. No other labels, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787143204-uSgjv5.jpg)

- **A.** The reaction is first order because \([\text{P}]\) decreases as the reaction proceeds.
- **B.** The reaction is first order because \([\text{P}]\) decreases from \(0.80\text{ M}\) to \(0.40\text{ M}\) during the first \(20\text{ min}\).
- **C.** The reaction is zero order because the instantaneous rate is directly proportional to \([\text{P}]\).
- **D.** The reaction is zero order because \([\text{P}]\) decreases by equal amounts during equal time intervals, so the slope remains constant.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119382/*