The scale drawing is 2cm : 1mm. Is the scale drawing larger or smaller than the actual object

Larger. the 1mm of actual object is shown as 2cm in the drawing.

Every 1 millimeter on the actual object is only 2 centimeters on the scale drawing.

(If you don't know which is which, think of the colon as "represents")

2 cm (=20 mm) is far larger than 1 mm, so the scale drawing must be larger.