Microscopic and macroscopic scales কী?

At the microscopic scale matter is made of molecules: $1\,\mathrm{mol}$ contains $N_A = 6.02 \times 10^{23}\,$ of them, each about $0.3\,\mathrm{nm}$ across; in a gas at ordinary conditions they are $3\,\mathrm{nm}$ apart, move at hundreds of meters per second and collide every $70\,\mathrm{nm}$ or so. At the macroscopic scale a system is described by a few state variables — pressure $P$, volume $V$, temperature $T$, amount of substance $n$ — that are averages over enormous numbers of molecules. A variable is extensive if it doubles when the system is doubled ($V$, $n$, mass, energy), intensive if it does not ($P$, $T$, density).