Mercury is a homogenous mixture of two or more pure substances
Answer:
a. neutron
Explanation:
A neutral atom has the same number of protons and electrons because in order for it to be a neutral atom the charges must be the same.
a neutron has no charge therefore it can be different then the number of protons and electrons in a neutral atom as it won't affect the charge.
Basically any animal group that doesnt have any backbones. for example fish birds different types of mammals and reptiles.
hope this helps!