**Core Concept**
The question is testing the pharmacological principle of atropine's cycloplegic effect, which is mediated by its anticholinergic action on the muscarinic receptors in the ciliary muscle of the eye. Atropine is a quaternary ammonium compound with a high molecular weight, which limits its absorption through mucous membranes.

**Why the Correct Answer is Right**
Atropine drops are used as cycloplegic agents in ophthalmology to temporarily paralyze the ciliary muscle, causing a loss of accommodation and allowing for accurate measurement of refractive errors. The cycloplegic effect of atropine is due to its ability to block the muscarinic receptors (M3 subtype) in the ciliary muscle, preventing the release of acetylcholine and subsequent contraction of the muscle. The concentration of atropine in atropine drops as a cycloplegic agent is typically around 1%.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the percentage of atropine present in atropine drops as a cycloplegic agent.

**Option B:** This option is incorrect because the percentage of atropine present in atropine drops as a cycloplegic agent is not 5%.

**Option D:** This option is incorrect because the percentage of atropine present in atropine drops as a cycloplegic agent is not 10%.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the cycloplegic effect of atropine is dose-dependent, and the percentage of atropine present in atropine drops can vary depending on the brand and formulation. The typical concentration of atropine in atropine drops as a cycloplegic agent is around 1%, and this should be taken into consideration when administering the medication.

**Correct Answer:** C. 1%