1 significant figure, because there is no decimal after the zero the zero doesn't count.
If the cube is 3 cm on each side, then it has a volume of 27 cm^3 (3 x 3 x 3). Density is mass divided by volume, so its density is 72.9/27 = 2.7 g/cm^3.
<span>Going by the density, the cube is made of Aluminium - density is a fairly unique quantity</span>
Hey there!
Exothermic reactions release heat, causing its temperature to fall. If the reaction is lessening the temperature of the object while releasing all the heat, then you know that the reaction is indeed exothermic. Hope this helps!