Second is the si base unit for measuring
a.)time
b.)length
c.)volume
d.)mass

a.)time

Explanation:

IN the international system time is measured in seconds, this is often used by scientifics more than regular people, since most of the measures of time that regular people use are often in hours or minutes, but for the international system the base for time is always in seconds.

in chemistry, a solution’s concentration is how much of a dissolvable substance, known as a solute, is mixed with another substance, called the solvent. the standard formula is c = m/v, where c is the concentration, m is the mass of the solute dissolved, and v is the total volume

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).