Explanation:
Given that,
Mass of metal cube, m = 20 g
Volume of cube, V =5 mL
We need to find the density of the cube. Mass per unit volume equals density.

So, the density of the cube is 4 g/ml.
We know that the density of Aluminium is 4 g/mL.
So, the cube is not Aluminium cube.
Atoms are indivisible spheres-Dalton model
John Dalton was the first to propose a theory to describe matter. As per Dalton's model, all matter is composed of atoms which resemble tiny 'ball-like' structures that are indivisible.
based on the law of conservation of energy its it atoms hold by strong chemical bonds
The given blank can be filled with isomers.
The isomers in chemistry refers to the molecules or ions with similar formulas, but different compositions. The isomers refer to the molecules that exhibit the same chemical formula, however, distinct three-dimensional shapes. Though isomers do not always share identical properties. The two prime forms of isomerism are stereoisomerism or spatial isomerism and structural isomerism or constitutional isomerism.