What is oxidation number of hg in k2(Hgl4)

Which element is least likely to undergo a chemical reaction

When the chemicals iron sulfide (fes) and hydrochloric acid (hcl) are combined, bubbles appear from the mixture. 1. does the appearance of bubbles indicate a physical or chemical change? 2. why do the bubbles indicate this change? 3. what property is this?

Ahelium balloon contains 16.9 l of helium at stp. how many atoms of helium are in the balloon