Answer : 1. "Electron-spin quantum number"
Explanation :

Many orbitals are possible in an atom. Qualitatively, these orbitals can be differentiated on the basis of their size, shape and orientation. Smaller orbitals mean that the probability of finding the electron closer to the nucleus is greater. Similarly, shape and orientation indicate that the probability of finding an electron is greater in one direction than in another. Atomic orbitals can be distinguished by quantum numbers. Each orbital is represented by three quantum numbers n, ℓ and m.