Out of the UV, green, blue, red and IR radiations which is most effective for causing photoelectric emission?

Why the alkali metals are most suitable for studying the photoelectric emission?

Which theory explains photoelectric effect?

What is photoelectric effect? Which metal can cause photoelectric emission with visible light?

Which of the following is most effective in causing the coagulation of ferric hydroxide sol?

The green house effect is caused by

Out of MgCl_2 and AlCl_3 , which one is more effective in causing coagulation of negatively charged sol and why?