**Core Concept**
ACE inhibitors are a class of medications used to treat hypertension and heart failure by blocking the conversion of angiotensin I to angiotensin II, thereby reducing vasoconstriction and decreasing blood pressure. This action also leads to a decrease in aldosterone-mediated sodium retention, resulting in increased potassium levels.

**Why the Correct Answer is Right**
The correct answer, "Decreases potassium concentration," is incorrect because ACE inhibitors actually increase potassium levels by reducing aldosterone-mediated sodium retention. Aldosterone stimulates the kidneys to retain sodium and excrete potassium, so by decreasing aldosterone levels, ACE inhibitors lead to increased potassium concentrations. This is a critical consideration in patients with renal artery stenosis or those taking other medications that affect potassium levels.

**Why Each Wrong Option is Incorrect**
**Option A:** Contraindicated in asthma is incorrect because ACE inhibitors are not typically contraindicated in asthma, although caution is advised in patients with a history of angioedema, a condition that can be precipitated by ACE inhibitors.

**Option B:** Lacks postural hypotension is incorrect because ACE inhibitors can cause postural hypotension, particularly in the initial stages of treatment, due to their vasodilatory effects.

**Option D:** Does not affect quality of life is incorrect because ACE inhibitors can affect a patient's quality of life by causing side effects such as cough, angioedema, and hyperkalemia (not decreased potassium levels).

**Clinical Pearl / High-Yield Fact**
ACE inhibitors can cause a dry cough in up to 20% of patients due to the accumulation of bradykinin, a potent vasodilator. This side effect is more common in patients taking ACE inhibitors and can often be managed with a change in medication.

**✓ Correct Answer: C. Decreases potassium concentration**