Arrange the following ions in order of increasing basicity and explain the order:
`CH_(3)overset(oplus)(C)H_(2)(I), " " CH-=overset(oplus)(C)(II), " " CH_(2)=overset(oplus)(C)H(III)`

Explanation

The order of increasing basicity of the given ions is:
`CH-=overset(Theta)(C)(II)ltCH_(2)=overset(Theta)(C)H(III)ltCH_(3)overset(Theta)(C)H_(2)(I)`
C - atoms bearing the negative charge in carbanious (I),(II) & (III) are `sp^(3),sp and sp^(2)` - hybridised respectively. Percentages of s - character of these three hybrid orbitals are 25%, 50% and 33% respectively. As the s - character of hybrid orbital increases, the hold of the carbanion - carbon on th unshared electron pair increases. Consequently, the availability of such electron pair for combination with a proton decreases and hence the basicity decreases. Therefore, among these three carbanions, (I) is more basic than (III) which in turn is more basic than (II).