A gold leaf electroscope is negatively charged and the leaves are observed to diverge by a certain amount. A beam of x-ray is allowed to fall upon the electroscope for a short period. The effect is as follows
A. The leaves will diverge further
B. There will be no change in the diverge
C. The leaves will collapse
D. The gold leaves will melt

Hint: We have to know about the gold leaf telescope to examine what happens when an x-ray beam is allowed to fall upon the electroscope.

Complete step by step answer:
An electroscope consists of a vertical metal rod that sticks out of a glass container; a strip of plastic stops the electrical charge from moving to the cylindrical container, which is normally metal, from the metal rod and metal leaves at the bottom.
Gold leaf electroscope- In a vacuumed glass jar and attached to a metal seal, the gold leaf electroscope has two gold leaves suspended from a metal stem. With the aid of a metal foil, the glass is grounded to keep it uncharged. It is possible to use it for: charge detection.
Charge detection: the body being examined under a gold leaf electroscope is touched by a metal cap. The body is charged if the leaves diverge, and if there is no impact on the leaves, then the body is not charged.
In this question, since the gold leaf electroscope is negatively charged, it can ionise the air around the gold leaf electroscope as the x-ray beam is allowed to land on the electroscope, as x-rays are the ionising radiation. As a consequence, the positive ions from the neighbouring environment would be drawn by negatively charged leaves and then discharged. The leaves will fall, as now there is no charge on the gold leaves.
Hence, option C is correct.

Note:We should be careful while using a gold leaf electroscope. The charge should be given from above and the sideways since it can make the gold leaves fall off.