The correct option is B 0.999 mm
Size of specimen 1:
There are 1 cube, 1 rod and 2 units.
This is equivalent to 1.012.
Size of specimen 2:
There are 2 cubes, 1 rod and 1 unit.
This represents 2.011
Hence, the difference in the size is,
= 2.011 - 1.012
= 0.999
Hence, the difference in the sizes of two specimen is 0.999 mm