This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pharmacology
which of the following is true regarding competitive reversible antagonism 
Select and explain. 
A. potency increases, B. Km decreases, C. efficacy and Vmax no change, D. ED50 decreases
C: efficacy and Vmax no change
Answer: C: efficacy and Vmax no change 
Explanation: COMPETITIVE Reversible ANTAGONISM 1.Same receptor by forming Weak bonds 2. Maximal response is concentration dependent 3.The effect of antagonist can be overcome by increasing the concentration of agonist 4. Parallel rightward shift of DRC COMPETITIVE Irreversible ANTAGONISM 1. Have affinity for the same receptor sites and bind in an irreversible manner by covalent bond 2. Effects cannot be overcome even by increasing the concentration of the agonist 3. LDR curves of agonist would show reduced efficacy but altered potency e.g. Dibenamine and NE at al adrenoceptors ref : kd tripathi 8th ed