The quantity, q grams, of the radioactive isotope strontium-90 present in a sample decreases by half over a period of about t = 28.8 years. if a sample initially contains 3 grams of strontium-90, what equation represents the relationship between q and t?

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?