Someone plz help me !!

Science
Or
Bias?

Which description best characterizes the motion of particles in a solid?

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?

Helium decays to form lithium. which equation correctly describes this decay?