Step 1: {Understanding concentration units}
Molarity \( (M) \) and normality \( (N) \) are volume-dependent, and volume fluctuates with temperature. In contrast, molality \( (m) \) is defined as: \[ m = \frac{{Moles of solute}}{{Mass of solvent in kg}} \] As mass is unaffected by temperature variations, molality is constant.
Step 2: {Why molality is temperature-independent}
Molality does not incorporate volume, which is susceptible to thermal expansion or contraction. Therefore, it is the preferred unit for temperature-dependent investigations.
A particle is moving in a straight line. The variation of position $ x $ as a function of time $ t $ is given as:
$ x = t^3 - 6t^2 + 20t + 15 $.
The velocity of the body when its acceleration becomes zero is: