Statement I: In Young's experiment, the fringe width for dark fringes is different from that of white fringes.
Statement II: In Young's doulbe-slit experiment, when the fringes are observed with a source of white light then only black and bright fringes are observed.

Options

A. Statement I is True, statement II is True, Statement II is a correct explanation for Statement I.
B. Statement I is Ture, Statement II is Ture, Statement II is NOT a correct explanation for Statement I.
C. Statement I is True, Statement II is False.
D. Statement I is False, Statement II is True.

Explanation

To analyze the given statements regarding Young's double-slit experiment, we will evaluate each statement step by step.

### Step 1: Evaluate Statement I
**Statement I:** In Young's experiment, the fringe width for dark fringes is different from that of white fringes.

1. **Understanding Fringe Width**: The fringe width (β) in Young's double-slit experiment is given by the formula:
\[ \beta = \frac{\lambda D}{d} \]
where \( \lambda \) is the wavelength of light, \( D \) is the distance from the slits to the screen, and \( d \) is the distance between the slits.

2. **Dark and Bright Fringes**: The fringe width is the same for both dark and bright fringes. This is because the positions of dark fringes are determined by the same fringe width formula, but at different orders of interference.

3. **Conclusion for Statement I**: Since the fringe width does not differ between dark and bright fringes, Statement I is **false**.

### Step 2: Evaluate Statement II
**Statement II:** In Young's double-slit experiment, when the fringes are observed with a source of white light, then only black and bright fringes are observed.

1. **Understanding White Light**: White light consists of multiple wavelengths (colors), each corresponding to a different wavelength of light.

2. **Fringe Formation with White Light**: When white light is used, each color will produce its own interference pattern. The positions of the bright and dark fringes will vary for each color due to their different wavelengths.

3. **Resulting Pattern**: Instead of only black and bright fringes, the interference pattern will show a spectrum of colors with overlapping bright fringes and dark fringes. Thus, we will see a series of colored fringes rather than just black and bright.

4. **Conclusion for Statement II**: Therefore, Statement II is also **false**.

### Final Conclusion
Both statements are false. Thus, the correct option is that both Statement I and Statement II are false.