Why is a block of gold is more dense than a block of iron of equal size?

Which describes increasing the efficiency of energy resource

You can melt ice by applying pressure because the solid/liquid line has a slope.

Relate the real life phenomenon with each branch physics; 1; mechanics 2; heat 3; sound 4; light(optics) 5; electricity& magnetism 6; atomic physics 7; nuclear physics 8; plasma physics 9; geophysics