According to vsepr theory, molecules adjust their shapes to keep which of the following as far apart as possible?
a. inner-shell electrons
b. the electrons closest to the nuclei
c. mobile electrons
d. pairs of valence electrons

d. pairs of valence electrons

Explanation:

Pair of valence electrons are kept as far apart as possible to avoid bond pair-bond pair repulsion. Each covalent bond is formed by the sharing of a pair of electrons. In its most stable 3D conformation a molecule will keeps its electron rich bonds far apart. For example, BeCl₂ has a linear structure where each of the Be-Cl bonds is 180° apart. Be has 2 valence electrons and can form a maximum of two covalent bonds.

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).