Explain why hydrogen gas is given off when a reactive metal undergoes a single-displacement reaction with water.

Hydrogen gas is given off when a reactive metal undergoes a single-displacement reaction with water is because the very active metals react with water. For example, calcium reacts with water to form calcium hydroxide and hydrogen gas etc. 

You would do 1500/4 and the answer is 375

Non metal is an element or substance that is not a metal metal is a solid material that is typically hard, shiny, malleable, fusible, and ductile, with good electrical and thermal conductivitymetalloid is an element (e.g., germanium or silicon) whose properties are intermediate between those of metals and solid nonmetals. they are electrical semiconductors.