**Core Concept**
The question tests the understanding of **inhalational corticosteroids**, specifically **beclomethasone**, and their common side effects. Beclomethasone is a synthetic **glucocorticoid** used in the treatment of **asthma** and **chronic obstructive pulmonary disease (COPD)**.

**Why the Correct Answer is Right**
The most common side effect of inhalational beclomethasone is **oropharyngeal candidiasis**, which occurs due to the **local immunosuppressive effects** of the corticosteroid on the mucosa, allowing **Candida** to overgrow. This side effect can be mitigated by rinsing the mouth after inhalation.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while **hoarseness** can be a side effect, it is not the most common.
**Option B:** Incorrect as **tremors** are more commonly associated with **beta-2 agonists**.
**Option D:** Incorrect because **hypokalemia** is not typically associated with inhaled corticosteroids.

**Clinical Pearl / High-Yield Fact**
Inhalational corticosteroids like beclomethasone can cause **local side effects** due to their direct contact with the respiratory mucosa, emphasizing the importance of proper inhaler technique and mouth rinsing post-use.

**Correct Answer:** D. Oropharyngeal candidiasis