The correct option is D narrower and brighter
The angular width of the entire central maximum is 2λa, where a is the width of the slit. If the value of a is doubled, the angular width of the central maximum decreases to half its earlier value.
This implies that the central maximum becomes much sharper.
Furthermore, when a is doubled, the intensity of the central maximum becomes four times. Thus, the central maximum becomes much sharper and brighter.
Hence, (B) is the correct answer.