The statement that describes why the expression is incorrect is:
"A neutron should be expressed as \( ^1_0n \), not \( ^0_1n \)."
In nuclear notation, the correct symbol for a neutron is typically written with a mass number of 1 (since a neutron has a mass of approximately 1 amu) and an atomic number of 0 (since it has no charge), resulting in the notation \( ^1_0n \). The expression \( ^0_1n \) is not the correct standard notation for a neutron.