$word_{count}$: 210

Solutions are homogeneous mixtures with concentration expressed in multiple units. Molarity (M = $\frac{mol}{L}$ solution) is the most commonly used but is temperature-dependent because volume changes with temperature. Molality (m = $\frac{mol}{kg}$ solvent) is temperature-independent and preferred for colligative property calculations. Mole fraction (x = mol component / total moles) is dimensionless and useful for Raoult's law and Henry's law. Mass percentage (w/w%) and parts per million (ppm) are mass-based and temperature-independent. Key interconversion: M to m requires density (d): m = 1000M / (1000d - M*$M_s$). For dilute aqueous solutions, m ≈ M since density ≈ 1 g/mL and solute mass is negligible. Mole fraction to molality: $x_2$ ≈ m*$M_1$/1000 (dilute limit). Molarity from density and mass%: M = 10dw%/$M_s$. Normality = M x n-factor. The choice of concentration unit matters for calculations: use molality for $delta_{Tb}$ and $delta_{Tf}$, mole fraction for RLVP and Raoult's law, and molarity for osmotic pressure. Misusing units is a common error in JEE problems — always check which property uses which concentration unit before calculating.