**Core Concept**
The Schwartz formula is a widely used method to estimate the glomerular filtration rate (GFR) in children. It takes into account the child's height and serum creatinine level to calculate the estimated GFR (eGFR). The formula is as follows: eGFR (mL/min/1.73 m^2) = (k x height in cm) / serum creatinine in mg/dL, where k is a constant that depends on the laboratory.

**Why the Correct Answer is Right**
The Schwartz formula is a reliable method for estimating GFR in children. In this case, the child's height is 85 cm, and serum creatinine is 2 mg/dL. We can plug these values into the formula to calculate the eGFR. However, we need to determine the value of k for our laboratory. The standard value of k is 0.413 for children. Using this value, we can calculate the eGFR as follows: eGFR = (0.413 x 85) / 2 = 17.5 mL/min/1.73 m^2.

**Why Each Wrong Option is Incorrect**
**Option A:** This option does not provide a valid formula for estimating GFR in children.
**Option B:** This option uses a different formula for estimating GFR, which is not relevant to the Schwartz formula.
**Option C:** This option does not provide a valid calculation for eGFR using the Schwartz formula.

**Clinical Pearl / High-Yield Fact**
The Schwartz formula is a useful tool for estimating GFR in children, but it requires accurate measurements of height and serum creatinine. It's essential to use the correct value of k for the laboratory and to consider other factors that may affect GFR, such as age, sex, and underlying medical conditions.

**Correct Answer: C. 17.5 mL/min/1.73 m^2**