The $$\mathrm{pK_a}$$ of acetylsalicylic acid (aspirin) is 3.5. The $$\mathrm{pH}$$ of gastric juice in human stomach is about 2-3 and the $$\mathrm{pH}$$ in the small intestine is about 8. Aspirin will be

Aspirin is a weak acid. For a weak acid, when $\mathrm{pH} < \mathrm{p}K_a$, the acid remains mostly in the unionized form, and when $\mathrm{pH} > \mathrm{p}K_a$, it is mostly in the ionized form. Here, $\mathrm{p}K_a = 3.5$. In the stomach, $\mathrm{pH} = 2\text{ to }3$, so $\mathrm{pH} < \mathrm{p}K_a$. Therefore aspirin is almost unionized there. In the small intestine, $\mathrm{pH} = 8$, so $\mathrm{pH} > \mathrm{p}K_a$. Therefore aspirin is ionized there. So the correct option is $\mathrm{D}$.