Which of the following ions has the maximum magnetic moment ?

Correct option is  (a) Mn²⁺  

Explaination :::

number of unpaired electrons in Mn²⁺  =5 
number of unpaired electrons in  Fe²⁺   =4 
number of unpaired electrons in Ti²⁺   =2
number of unpaired electrons in Cr²⁺ =4

Magnetic moment =\(\sqrt{n(n+2)} B.M.\)   … Here "n" is the number of unpaired electrons .

The maximum number of unpaired electrons are in  Mn²⁺   that is 5  therefore maximum magnetic moment is of Mn²⁺ ion

Hence , (a) Mn²⁺   is correct