The correct answer is: D. The structure of atoms is different.
Allotropes are different forms of the same element that have different physical properties. For example, carbon has two common allotropes: diamond and graphite. Diamond is a hard, transparent solid, while graphite is a soft, black solid. The difference in properties between these two allotropes is due to the different ways in which the carbon atoms are arranged in their crystal structures.
In diamond, each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement. This gives diamond its strong, rigid structure. In graphite, each carbon atom is bonded to three other carbon atoms in a planar arrangement. This gives graphite its soft, flaky structure.
The number of electrons, bonds, and neutrons in an element does not change between allotropes. It is only the structure of the atoms that is different.
Explanation of each option:
- A. The number of electrons is different.
This is not the correct answer because the number of electrons in an element does not change between allotropes. For example, both diamond and graphite are made of carbon atoms, which have six electrons in their outer shell.
- B. Bonds are of different types.
This is not the correct answer because the type of bonds in an element does not change between allotropes. For example, both diamond and graphite are made of carbon atoms that are bonded to each other by covalent bonds.
- C. The number of neutrons varies.
This is not the correct answer because the number of neutrons in an element does not change between allotropes. For example, both diamond and graphite are made of carbon atoms that have six protons and six neutrons in their nucleus.
- D. The structure of atoms is different.
This is the correct answer because the structure of the atoms in an element is different between allotropes. For example, in diamond, each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement. In graphite, each carbon atom is bonded to three other carbon atoms in a planar arrangement.