Explanation:
1. The mass of a substance per unit volume: Density
Higher density means the atoms are closely packed.
2. a proposed explanation for a scientific problem: Hypothesis
Before a problem is solved with an experimental or theoretical proof a hypothesis is given which is a probable solution for the problem. This hypothesis might be proved wrong at a later stage but it still works as a starting point to find a solution.
3. standard metric unit of length : Meter
The standard unit to measure the length.
4. standard metric unit of mass: Kilogram
The standard unit to measure the mass.
5. anything that has mass and occupies space: Matter
6. a quantity in an experiment that remains un-changed or constant: Control
