The organisms that can grow on stones and help in soil formation are (a) lichens and (b) mosses.
Explanation:
Lichens:
These symbiotic organisms, consisting of a fungus and algae, can colonize bare rocks and release chemicals that break down the rock surface, creating a thin layer of soil where other plants can then establish themselves.
Mosses:
Like lichens, mosses can also grow on rocks and contribute to soil formation by trapping moisture and releasing substances that help weather the rock surface, allowing for the development of a more fertile environment.
Why other options are incorrect:
(c) Mango tree:
Mango trees are large trees that require well-established soil to grow. They cannot thrive on bare rocks and are not considered significant contributors to soil formation.
(d) Cactus:
Cacti are adapted to arid environments and grow in sandy or rocky soils, but they do not actively contribute to the breakdown of rocks or the formation of new soil.