1. In Young’s double slit experiment, the fringe width is given by

$\beta = \frac{\lambda D}{d}$

where:

• $\lambda$ = wavelength of light
• $D$ = distance between slit and screen
• $d$ = separation between slits

2. When the source changes from orange to blue, the wavelength decreases because blue light has a smaller wavelength than orange light:

$\lambda_{\text{blue}} < \lambda_{\text{orange}}$

3. Since fringe width $\beta$ is directly proportional to wavelength $\lambda$,

$\beta \propto \lambda$

therefore, on changing from orange to blue,

$\beta_{\text{blue}} < \beta_{\text{orange}}$

So the distance between consecutive fringes decreases.

4. Now check the options:

• A: Central bright fringe will become dark fringe.
  False. The central fringe remains bright because path difference at the center is zero.

• B: Distance between consecutive fringes will decrease.
  True.

• C: Distance between consecutive fringes will increase.
  False.

• D: Intensity of minima will increase.
  False. Ideal minima remain zero intensity in YDSE.

Therefore, the correct option is:

$\boxed{\text{B}}$