The Relationship Between Structure and Acidity

why are the Acidity increases going down a row of the periodic table?
answer : according my opinion and acidity increases going left to right (because more electronegative atoms can stabilize the negative charge on the anion) and increases going down because the larger the atom the better it can delocalize the negative charge.

Nucleophicity and basicitiy tend to be similar to each other but opposite to electrongegativity trends. Nucleophicity increases going left across a period and up a group.

The Electron affinity of a molecule or atom is the energy change when an electron is added to the neutral atom to form a negative ion. This property can only be measured in an atom in gaseous state.

X + e− → X−

The electron affinity, Eea, is defined as positive when the resulting ion has a lower energy, i.e. it is an exothermic process that releases energy:

Eea = Einitial − Efinal

Alternatively, electron affinity is often described as the amount of energy required to detach an electron from a singly charged negative ion[1], i.e. the energy change for the process

X− → X + e−

A molecule or atom that has a positive electron affinity is often called an electron acceptor and may undergo charge-transfer reactions.
Contents
Although Eea varies greatly across the periodic table, some patterns emerge. Generally, nonmetals have more positive Eea than metals. Atoms whose anions are more stable than neutral atoms have a greater Eea. Chlorine most strongly attracts extra electrons; mercury most weakly attracts an extra electron. The electron affinities of the noble gases have not been conclusively measured, so they may or may not have slightly negative values.

Eea generally increases across a period (row) in the periodic table. This is caused by the filling of the valence shell of the atom; a group 7A atom releases more energy than a group 1A atom on gaining an electron because it obtains a filled valence shell and therefore is more stable.

A trend of decreasing Eea going down the groups in the periodic table would be expected. The additional electron will be entering an orbital farther away from the nucleus, and thus would experience a lesser effective nuclear charge. However, a clear counterexample to this trend can be found in group 2A, and this trend only applies to group 1A atoms. Electron affinity follows the trend of electronegativity. Fluorine (F) has a higher electron affinity than oxygen and so on.