How many moleciles are there in 2.3 grams of NH4SO2

A6.10 m nacl can be made by adding [x]g of nacl to a container and making the volume of water up to the 1.00 l line

What is the molar mass of a gas that has density of 2.054 g/l

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?