One half of the distance between the nuclei of two adjacent metal atoms in the close packed crystal lattice is called what?

Summarize possible ways in which phases of matter could combine to form a solution.

Which element has the lowest electronegativity? calcium(ca) gallium(ga) selenium(se) bromine(br)

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?