This question was not popular among the candidates and the performance of those who answered the question was poor. The candidates could not easily differentiate between plutonic and volcanic rocks. The expected answers included:
-   plutonic rocks are formed beneath or within the earth’s crust while volcanic rocks are formed on the surface of the earth
-   Plutonic rocks have large crystals while volcanic rocks have small crystals
-   plutonic rocks are coarse grained while volcanic rocks are fine grained
-   plutonic rocks are also called intrusive rocks while volcanic rocks are also called extrusive rocks
-   plutonic rocks are mostly basic rocks while volcanic rocks are acidic rocks
-   during the process of formation, cooling is slower for plutonic rocks while it is faster for volcanic rocks
-   landforms associated with plutonic rocks are batholites, sills and dykes while those associated with volcanic rocks are composite cones, lava plateaux, etc
-   examples of plutonic rocks include, granite, diorite, and gabbro, whilst examples of volcanic rocks include basalt, rhyolite, andesite and obsidian.
           
The mode of formation of crater lake is as follows:

-   weakness develops in earth crust
-   molten magma is trapped within the earth crust
-   cracks and joints develop in the areas of crustal weakness
-   magma under pressure is ejected through a vent
-   magma is composed of ash and cinder
-   a cone is built around the vent by the materials
-   the vent is blocked
-   subsequent eruptions blow off the top of the cone
-   a depression is formed
-   the depression is called crater
-   rain water/melting ice collects in the crater
-   this forms a crater lake
-   subsequent forcefull eruptions blow off the top of the cone and the crater
-   a larger depression called caldera is created
-   water collects in the caldera to form a caldera lake
-   e.g. Lake Payam in Jos Plateau, Nigeria; Lake Bosumtwi near Kumasi, Ghana; Blue lake in Australia; Lake Shala in Ethiopia; Lake Toba in Sumatra, Lake Oregon in USA.