The correct option is C 0.001
The decimal numbers can be converted to fraction form by shifting the decimal point three times to the right to obtain the whole number.
Therefore, 0.101, 0.010, 0.001 and 0.011 can be expressed as 1011000, 101000, 11000, and 111000 respectively.
Comparing the numerator part of the fractions we find that 1 is the smallest amongst the four. Therefore, the decimal number 0.001 is the smallest decimal number