**Core Concept**
Cystic fibrosis (CF) is an autosomal recessive genetic disorder caused by mutations in the CFTR gene, leading to abnormal chloride transport across epithelial cell membranes. This results in thick, sticky mucus accumulation in various organs, primarily the lungs and pancreas.

**Why the Correct Answer is Right**
In autosomal recessive inheritance, an individual must inherit two mutated alleles (one from each parent) to express the disease. If only one parent is affected (homozygous recessive) and the other is normal (homozygous dominant), each child has a 50% chance of inheriting the mutated allele from the affected parent. This makes the child a carrier (heterozygous) but does not express the disease themselves. However, if the child inherits two mutated alleles (one from each parent), they will express the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it implies a 25% chance, which is not consistent with autosomal recessive inheritance.

**Option B:** This option is incorrect because it suggests a 100% chance, which is not possible in autosomal recessive inheritance unless both parents are carriers.

**Option C:** This option is incorrect because it implies a 0% chance, which is not consistent with the possibility of inheriting the mutated allele from the affected parent.

**Clinical Pearl / High-Yield Fact**
In autosomal recessive disorders, carriers (heterozygous individuals) are generally asymptomatic but can pass the mutated allele to their offspring, who may express the disease.

**Correct Answer: B. 25%**