Which molecule is secreted from the peritubular capillary network into the convoluted tubules?

The correct answer is  H+.
Secretion from the peritubular capillary network into the convoluted tubules is a process called tubular secretion. This is an important process for both waste removal and acid-base balance. The secretion step is usually used to remove drugs, toxins, and poisons, or other molecules such as potassium (K+) and hydrogen (H+). The secreted molecules come from the peritubular capillaries and pass through the interstitial fluid before going through the wall of the tubule into the lumen of the tubule.

I’m going to go with b!