Orbitals are regions or spaces where there is a maximum probability of finding electrons. Qualitatively, these orbitals can be distinguished by their size, shape, and orientation. An orbital of small size means there is more chance of finding the electron near the nucleus. Shape and orientation mean the direction in which the probability of finding the electron is maximum. Atomic orbitals can be distinguished by quantum numbers. Each orbital is designated by three quantum numbers n, l, and ml (magnetic quantum number) which define energy, shape, and orientation but these are not sufficient to explain spectra of multi-electrons atoms. Spin quantum number (ms ) determines the spin of electrons. Spin angular momentum of the electron has two orientations relative to the chosen axis which are distinguished by spin quantum numbers ms which can take values +1/2 and –1/2. (a) How many orbitals are associated with n = 3?(b) Describe the orbitals represented by (i) n = 2, l = 1 (ii) n = 4, l = 0. (c) (c) How many electrons are possible in an orbital? Why?d) What is the shape of ‘s’ and ‘p’ orbitals? (e) Name two d-orbitals that are on-axis.​