Question

What is the volume of a pebble

Answer 1

One way to measure the volume of any irregular object (in your case, a stone) is to submerge it completely under water and measure the change in the height of the water level. This change in the water level (let's say it goes from 50 mL to 65 mL) indicates that the stone has a volume of 15 mL.

Answer 2

Volume of pebble = final volume - initial volume = 27-25 = 2ml