What is the difference between a strong acid and a weak acid with examples?

Strong and weak refer to how completely an acid ionises in water, not how dangerous it is. A strong acid ionises almost fully, releasing nearly all its H+ ions. Examples are hydrochloric acid (HCl), sulphuric acid (H2SO4) and nitric acid (HNO3). A weak acid ionises only partly, so most of it stays as whole molecules and releases fewer H+ ions. Examples are acetic acid (in vinegar) and carbonic acid (in soda water). For the same concentration, a strong acid has a lower pH because of more H+ ions. So concentration is about how much acid is dissolved, while strength is about how much of it actually splits into ions. A dilute strong acid can be milder than a concentrated weak one.