61. Using the symbol of the previous noble gas to indicate the core electrons, write the electron configuration for each of the fol-
lowing elements.
a. scandium, Z= 21 c. lanthanum, Z= 57
b. yttrium, Z = 39
d. actinium, Z= 89

Scandium, with atomic number of 21 = [Ar]3d¹4s²

Yttrium, with atomic number of 39 = [Kr]4d¹5s²

Lanthanum, with atomic number of 57 = [Xe]5d¹6s²

Actinium, with atomic number of 89 = [Rn]6d¹7s²

Explanation:

The electronic configuration of atoms of elements describes how electrons are arranged in the atomic orbitals of the atom. The electron configurations of atoms in standard notation is usually written sequentially with all electron-containing atomic subshells (s, p, d and f) and the number of electrons they contain in superscript. For example, the electron configuration of Neon is 1s²2s²2p⁶. However, an abbreviated notation can be used especially for elements having large atomic numbers. The symbol of the previous noble gas in square brackets indicating the core electrons is written before the outermost shell electrons of the atom. For example, the abbreviated electron configuration of sodium is [Ne]3s¹.

The electronic configuration of the given elements are shown below:

Scandium, with atomic number of 21 = [Ar]3d¹4s²

Yttrium, with atomic number of 39 = [Kr]4d¹5s²

Lanthanum, with atomic number of 57 = [Xe]5d¹6s²

Actinium, with atomic number of 89 = [Rn]6d¹7s²

the electrical  conductivity  of asolution  of an electrolyte is measured by determining the resistance of thesolution  between two flat or cylindrical electrodes separated by a fixed distance.