B

Step 1: Calculate the difference in lengths of rods A and B.
The lengths are given as:
Length of rod A = 3.25 ± 0.01 cm
Length of rod B = 4.19 ± 0.01 cm

Step 2: Find the difference:
Length of rod B - Length of rod A = 4.19 - 3.25 = 0.94 cm.

Step 3: Determine the uncertainties:
The uncertainty in the difference can be calculated by adding the uncertainties of both measurements:
Uncertainty in A = 0.01 cm
Uncertainty in B = 0.01 cm

Therefore, total uncertainty = 0.01 + 0.01 = 0.02 cm.

Step 4: Express the result:
The difference in lengths is 0.94 cm with an uncertainty of 0.02 cm. Thus, we have:
Difference = 0.94 ± 0.02 cm.

Step 5: Choose the correct option: Among the options provided, the one that matches the calculated difference and its uncertainty is option B: 0.94 ± 0.01 cm.
Therefore, the correct answer is B.