Which rock is composed of the mineral halite that formed when seawater evaporated?
(1) limestone (3) rock gypsum
(2) dolostone (4) rock salt

The correct answer is (4)

Halite is the natural form of salt  commonly referred to as rock salt.  It is a common and well known mineral and is found in solid masses, and as dissolved solution in the oceans and in salt lakes.

The inland lakes that are rich in salt exist in arid regions, and may also be below sea level without an outlet. These lakes evaporate during dry seasons, causing a recession in the water level and an icrease in salinity content.

When this happens, salt forms on the evaporated shores of the lake.