(2) My nails are about 1 cm wide;

(3) The length of a piece of chalk is 1 decimeter;

(4) Xiaoming's height1.35cm;

(5) The credit card is about 1mm thick;

(6) My pencil is about 2 centimetres long;

The school track is 300 meters long.

So the answer is: decimeter, centimeter, centimeter, decimeter, meter, centimeter, millimeter, decimeter, meter.