. Which one of the following ionic species has the greatest proton

Best Answer

Correct Option is: A

➔ Higher the proton affinity, the stronger the base and the weaker the conjugate acid. ➔ On moving towards right in a period in the periodic table, the basicity (proton affinity) decreases as the electronegativity of the atom possessing the lone pair of electrons increases. For this reason, NH₂^- is a stronger base than F^-. 

➔ On moving down a group, basicity decreases due to increase in the atomic size. Hence basicity of I- < F^-.