**Core Concept**
The absorption of drugs from the gastric mucosa depends on their lipophilicity, ionization state, and the presence of specific transport mechanisms. Drugs that are weakly acidic or neutral, and have a molecular weight below 500 Da, are more likely to be absorbed from the stomach.

**Why the Correct Answer is Right**
Diclofenac sodium is a weakly acidic nonsteroidal anti-inflammatory drug (NSAID) with a molecular weight of 318.14 g/mol. Its lipophilic nature and acidic pKa (3.8) facilitate its absorption from the gastric mucosa. The stomach's acidic environment helps to ionize diclofenac, making it more lipophilic and thus more easily absorbed. Additionally, diclofenac can be absorbed through passive diffusion and possibly through specific transport mechanisms like the monocarboxylate transporter 1 (MCT1).

**Why Each Wrong Option is Incorrect**
**Option A:** Morphine sulfate is a weak base with a pKa of around 7.8, making it more ionized in the acidic stomach environment, which reduces its absorption.
**Option C:** Hyoscine hydrobromide is a quaternary ammonium compound, making it highly charged and poorly absorbed from the stomach.
**Option D:** Quinine dihydrochloride is a weak base with a pKa of around 8.4, which also reduces its absorption from the stomach due to ionization.

**Clinical Pearl / High-Yield Fact**
When considering gastric mucosa absorption, remember that weakly acidic or neutral, lipophilic drugs with molecular weights below 500 Da are more likely to be absorbed.

**✓ Correct Answer: B. Diclofenac sodium**