Question

Which of the following is basic?
A.${F_2}$
B.$C{l_2}$
C.$B{r_2}$
D.${I_2}$

Answer 1

Hint: Base is a substance which can donate lone pairs of electrons. Also, basicity is inversely proportional to the electronegativity.

Complete step by step answer:
We know that the base is a substance which can donate electron pairs easily. So, basicity is inversely proportional to the electronegativity. If the electronegativity is higher, it will attract its lone pairs towards it and it is difficult to donate. So, the molecule with low electronegativity will have more free lone pairs and can easily donate. Among the four options, ${F_2}$ have the highest electronegativity. So, ${F_2}$ molecule cannot donate electrons easily and less basic. Down the group in a periodic table, electronegativity decreases. So, ${I_2}$ have low electronegativity and hence more basic.
 Therefore, the correct option is (D).

Additional Information:
According to Arrhenius theory, acid is a substance that gives ${H^ + }$ ion on dissolving in the aqueous solution. It increases the concentration of ${H^ + }$ ions in the solution. The base is a substance that ionizes $O{H^ - }$ ions in aqueous solution. The concentration of $O{H^ - }$ is high in the solution.
According to Bronsted-Lowry theory, acid is a substance which donates an ${H^ + }$ ion or a proton and forms its conjugate base and the base is a substance which accepts an ${H^ + }$ ion or a proton and forms its conjugate acid.

Note: Fluorine is the highest electronegative element in the periodic table. Therefore, it cannot donate electron pairs easily. Always remember that electronegativity is inversely proportional to the basicity.