What is the lightest semi-metal on the periodic table?

lithium

Lightest Elemental Metals

The lightest or least dense metal that is a pure element is lithium, which has a density of 0.534 g/cm3. This makes lithium nearly half as dense as water, so if lithium was not so reactive, a chunk of the metal would float on water.

Explanation:

this protocol provides a detailed procedure for co-immunoprecipitation (co-ip) to identify protein–protein interactions.

sulfur dioxide

explanation: acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. these substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.