A student was given four unknown colourless samples labelled A, B, C and D and asked to test their pH using pH paper. He observed that the colour of pH paper turned to light green, dark red, light orange and dark blue with samples A, B, C, and D respectively. The correct sequence of increasing order of the pH value of samples is

Options

A. `A lt B lt C lt D`
B. `A lt D lt C lt B`
C. `C lt B lt A lt D`
D. `B lt C lt A lt D`

Answer

To determine the correct sequence of increasing order of the pH values of samples A, B, C, and D based on the color changes observed on the pH paper, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Color Changes and Corresponding pH Values:**
- Sample A: Light Green
- Sample B: Dark Red
- Sample C: Light Orange
- Sample D: Dark Blue

2. **Interpret the Color Changes:**
- **Light Green** indicates a neutral pH, which is around 7.
- **Dark Red** indicates a highly acidic solution, likely with a pH around 1.
- **Light Orange** indicates a less acidic solution, with a pH greater than 1 but still less than 7.
- **Dark Blue** indicates a strongly basic solution, with a pH significantly greater than 7.

3. **Determine the pH Values:**
- Sample A (Light Green) = pH ≈ 7
- Sample B (Dark Red) = pH ≈ 1 (highly acidic)
- Sample C (Light Orange) = pH > 1 and < 7 (acidic)
- Sample D (Dark Blue) = pH > 7 (basic)

4. **Arrange the Samples in Order of Increasing pH:**
- The order of increasing pH values based on the interpretations:
- Sample B (Dark Red) < Sample C (Light Orange) < Sample A (Light Green) < Sample D (Dark Blue)

5. **Final Sequence:**
- The correct sequence of increasing order of the pH values of the samples is:
- B < C < A < D