**Core Concept**
Cystic fibrosis is an **autosomal recessive disorder**, meaning that a person must inherit two defective copies of the **CFTR gene** (one from each parent) to express the disease. The **genotype** of an individual with cystic fibrosis is homozygous recessive.

**Why the Correct Answer is Right**
If only one parent is affected, they must be homozygous recessive for the disease-causing allele. The other parent, being normal, is likely homozygous dominant or a carrier (heterozygous) for the **CFTR gene**. Each child has a 50% chance of inheriting the diseased allele from the affected parent and a 50% chance of inheriting a normal allele from the other parent, making them a carrier. However, the chance of a child inheriting two diseased alleles (one from each parent) and thus expressing cystic fibrosis is lower.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it overestimates the risk.
**Option B:** This option is also incorrect as it does not accurately reflect the genetic risk.
**Option D:** This option underestimates the risk and is not consistent with **autosomal recessive inheritance**.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that carriers of **autosomal recessive disorders** are generally asymptomatic but can pass the mutated gene to their offspring.

**Correct Answer:** C. 0% chance if the other parent is normal, as the question implies the other parent does not carry the mutated gene.