Which of the following are true for a single slit diffraction?
(A) Width of central maxima increases with increase in wavelength keeping slit width constant.
(B) Width of central maxima increases with decrease in wavelength keeping slit width constant.
(C) Width of central maxima increases with decrease in slit width at constant wavelength.
(D) Width of central maxima increases with increase in slit width at constant wavelength.
(E) Brightness of central maxima increases for decrease in wavelength at constant slit width.

Explanation:
Let us derive the correctness of each statement using the standard formula for single slit Fraunhofer diffraction:

The linear width of the central maximum is given by the expression:
\( \beta = \frac{2\lambda D}{a} \)
Where \( \lambda \) is the wavelength of light, \( D \) is the distance between the slit and the screen, and \( a \) is the width of the slit.

1. Analysis of Statement (A) and (B):
From the formula, the width of the central maximum is directly proportional to the wavelength of light \( (\beta \propto \lambda) \). Therefore, if the wavelength increases, the width of the central maximum increases. This makes statement (A) correct and statement (B) incorrect.

2. Analysis of Statement (C) and (D):
The width of the central maximum is inversely proportional to the slit width \( (\beta \propto \frac{1}{a}) \). Therefore, if the slit width decreases, the width of the central maximum increases. This makes statement (C) correct and statement (D) incorrect.

3. Analysis of Statement (E):
The peak intensity (brightness) of the central maximum depends on the square of the slit width \( (I \propto a^2) \) and is independent of the wavelength of the incident light. Therefore, statement (E) is incorrect.

Since only statements (A) and (C) are true, the correct combination is A, C only.

Hence, Option B is the correct choice.