Question

Which is an example of physical weathering?
Responses

a crack in rock growing larger as water freezes in it
a crack in rock growing larger as water freezes in it - no response given

bits of iron in rock rusting when exposed to oxygen and water
bits of iron in rock rusting when exposed to oxygen and water - no response given

microscopic organisms producing compounds that break down rock
microscopic organisms producing compounds that break down rock - no response given

lichen releasing a weak acid that dissolves rock

Answer 1

A crack in rock growing larger as water freezes in it.

Explanation: That's frost wedging — water expands when it freezes and physically forces the rock apart (mechanical weathering). The other examples involve chemical changes (rusting, acids produced by organisms), so they are chemical or biochemical weathering.