Which of the following produces citric acid(1) Lactobacillus acidophilus(2) Aspergillus niger(3) Mucor (4) both (3) and (4)

Citric acid is produced by various microorganisms such as Aspergillus niger, Penicillium restrictum, Trichoderma viride, Mucor piriformis, A. awamori. A. niger is one of the most commonly used source for citric acid production so ans is 4)