The sperms employed for artificial insemination of cattle are stored in ...............

The correct option is D Liquid nitrogen
Artificial insemination (AI) is a globally accepted method of breeding cattle and is also effective for other species. An estimated worldwide total of 150 million cows are artificially inseminated. Semen can be stored deep-frozen in liquid nitrogen (N${}_2$), in a chilled liquid form or at room temperature. Hence, option D is correct.