Solve this :
1. Red light, however bright, cannot cause emission of electron from a clean zinc surface. But even weak ultraviolet radiations can do so. Why ?
2. Name the series of hydrogen spectrum lying in the ultraviolet region.
Kindly ask different queries in different thread. Also, refer the similar link of 2nd question.
https://www.meritnation.com/ask-answer/question/which-series-of-hydrogen-spectrum-lies-in-i-visible-reg/classification-of-elements-and-periodicity-in-properties/7161015
https://www.meritnation.com/ask-answer/question/which-series-of-hydrogen-spectrum-lies-in-i-visible-reg/classification-of-elements-and-periodicity-in-properties/7161015