The correct answer to that question is 7.
You are possibly thinking of 'cumulo-nimbus' clouds
In science, "puffy white clouds" are known as cumulus clouds.
burimbus
white and puffy
the ones in the sky
cumulus cloud
CUMULUS
Cumulous
The clouds that are puffy masses formed by vertically rising air are commonly known as thunderheads. These clouds, with the scientific name of cumulonimbus, may produce severe weather such as lightning, hail, and even tornadoes.
they may be......afids
A thunder cloud, or Cumulonimbus cloud, looks like a massive, tall, white puffy cloud with an anvil shaped top and a very dark grey base.