The answer is (B)
Method:
1)The numerator of the fraction is obtained by subtracting the non-recurring figure from the given figure.
2)The denominator consists of as many 9's as there are recurring figures and as many zeros as there are non recurring figures.
Here the number is 0.4232323......
So 0.423=(423-4)/990=419/990 because 4 is non-recurring and there are two recurring figures(2and 3).