Copolymer, dispersant, and resin composition

A copolymer consisting of:

• a (meth)acrylic monomer unit A having an anionic group;
• a (meth)acrylic monomer unit B having a cationic group;
• and
• a (meth)acrylic monomer unit C other than the (meth)acrylic monomer unit A and the (meth)acrylic monomer unit B, wherein the (meth)acrylic monomer unit C comprises one or more selected from the group consisting of oxyalkylene skeletons, siloxane skeletons, and phosphodiester skeletons,
• wherein:
• a content of the (meth)acrylic monomer unit A is from 0.03 to 70 mol % based on a total of 100 mol % of the (meth)acrylic monomer unit A, the (meth)acrylic monomer unit B, and the (meth)acrylic monomer unit C;
• a content of the (meth)acrylic monomer unit B is from 0.02 to 20 mol % based on a total of 100 mol % of the (meth)acrylic monomer unit A, the (meth)acrylic monomer unit B, and the (meth)acrylic monomer unit C;
• a content of the (meth)acrylic monomer unit C is from 30 to 99.8 mol % based on a total of 100 mol % of the (meth)acrylic monomer unit A, the (meth)acrylic monomer unit B, and the (meth)acrylic monomer unit C;
• and
• the copolymer has a weight-average molecular weight of from 5,000 to 500,000 g/mol.