The statement below is followed by four options. Each option is related to the item in the statement, but only one is always true. Select the option that always holds and makes the statement true.
"A gas always has ______."
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → No fixed shape
The answer must hold for every gas, without exception. An option that is present in most cases but can be missing in even one case is not always true.
Option (1) A colour — oxygen and nitrogen are colourless.
Option (2) A smell — oxygen has no smell.
Option (3) No fixed shape — a gas has neither a fixed shape nor a fixed volume; it spreads to fill whatever container holds it, so this is always true.
Option (4) Less weight than an equal volume of air — carbon dioxide is heavier than air; that is why it settles over a fire and is used to put it out.