Using NSBaselineOffsetAttributeName solved my problem,Using this we can specify the offset from the bottom.+ve for superscript and -ve for subscript
-(void)setText:(id)text withPrefixText:(id)prefixText andSuffixText:(id)suffixText
{
NSString * compondText = [self textByCompoundingText:text withPrefixText:prefixText WithsuffixText:suffixText];
NSMutableAttributedString * attributedCompoundText = [[NSMutableAttributedString alloc] initWithString:compondText];
NSMutableDictionary * prefixTextAttributes = [@{} mutableCopy];
prefixTextAttributes[NSFontAttributeName] = _prefixTextFont? _prefixTextFont:self.font;
prefixTextAttributes[NSForegroundColorAttributeName] = _prefixTextColour? _prefixTextColour:self.textColor;
NSNumber *baselineOffSet =[NSNumber numberWithUnsignedInteger:_prefixTextVerticalPositionning];
prefixTextAttributes[(NSString*)NSBaselineOffsetAttributeName] = baselineOffSet;
NSMutableDictionary * suffixTextAttributes = [@{} mutableCopy];
suffixTextAttributes[NSFontAttributeName] = _suffixTextFont? _suffixTextFont:self.font;
suffixTextAttributes[NSForegroundColorAttributeName] = _suffixTextColour ?_suffixTextColour:self.textColor;
baselineOffSet = [NSNumber numberWithUnsignedInteger:_suffixTextVerticalPostioning];
suffixTextAttributes[(NSString*)NSBaselineOffsetAttributeName] = baselineOffSet;
if(prefixText)
[attributedCompoundText addAttributes:prefixTextAttributes range:[compondText rangeOfString:prefixText]];
if(suffixText)
[attributedCompoundText addAttributes:suffixTextAttributes range:[compondText rangeOfString:suffixText]];
self.attributedText = attributedCompoundText;
}