The part of an experiment used for standard comparison

Scientific Method

Explanation:

In a scientific method, the control is the group that serves as the standard of comparison. The control group may be a “no treatment" or an “experimenter selected” group. The control group is exposed to the same conditions as the experimental group, except for the variable being tested.

igneous rocks are formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.  

the composition depends on the source magma. there are almost a thousand types of composition found till now.  

hope this

other quantities, called derived quantities, are defined in terms of the seven base quantities via a system of quantity equations. the si derived unitsfor these derived quantities are obtained from these equations and the seven si base units.