electron affinity of lithium is -60 whereas of cesium is -45.this trend is due to... plz give me accurate answer

Electron affinity is defined as the change in energy (in kJ/mole) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion. In other words, the neutral atom's likelihood of gaining an electron.

Electron Affinity of Lithium is 59.6 kJ/mol.

Electron Affinity of Caesium is 45.5 kJ/mol.

Electron Affinity of Lithium is 59.6 kJ/mol. Electronegativity of Lithium is 0.98. ... Electron affinities are more difficult to measure than ionization energies. An atom of Lithium in the gas phase, for example, gives off energy when it gains an electron to form an ion of Lithium.

Trends

The ionization energy of the elements within a period generally increases from left to right. This is due to valence shell stability.

The ionization energy of the elements within a group generally decreases from top to bottom. This is due to electron shielding.

The noble gases possess very high ionisation energies because of their full valence shells as indicated in the graph. Note that helium has the highest ionization energy of all the elements.

The mass has escaped into a gas which you can not see so the law stays true.