When you see an image of a solid the particles of the solid are usually packed but in fact there may be some between them.

When you see an image of a solid the particles of the solid are usually packed tight but in fact there may be some space between them.

1. tight/tightly

2. movement/space

answer: mercury

explanation:

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.