I need help on these questions?

Which substances have the lowest melting points: ionic covalent, or metallic

Modern weaponry has increased the number of deaths in wars and violent conflicts.

Three cards with holes are arranged in a straight line. a light is shined through the first card’s hole and travels through all three cards. what does this tell you about light rays? a) that light is reflected b) that light is refractive c) that light travels in a straight line d) that light does not travel in a straight line