Consider the hypothetical molecule abcd. four structures can be drawn for this molecule with the following formal charges.
structure one: a and b have formal charges of +1, whereas c and d have formal charges of -1.
structure two: a and b have formal charges of +2, whereas c and d have formal charges of -2.
structure three: all four atoms have formal charges of zero.
structure four: a and b each have a formal charge of 0, whereas c and d have formal charges of +1 and -1, respectively.
which is the best lewis structure for molecule abcd?

The correct option from the given formula ABCD is the first option out of the four given choices.

Explanation:

The valence electrons are responsible for the formation of a compound lack of electrons in the valence shell of one element and presence of electron in other which both can share.

Now the first option use that the lack of electron in first element is 100 has a positive charge while the other one has one negative charge but share the  electron making both the elements stable in form of a new compound.

"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."

aquifers are bounded above and below by impermeable rock. the driving force of groundwater movement in confined aquifers is pressure, rather than gravity.