Ans. (a) Solid mediumRef: Microbiology by Ananthanarayan and Paniker 8th ed. / 39-40GROWING BACTERIAL CULTURES IN LIQUIDNUTRIENT BROTH* Nutrient broth is a liquid bacterial growth medium made of powdered beef extract and short chains of amino acids that have been dissolved in water.* Liquid medium is convenient to use for growing bacteria in test tubes, and can reveal information about the oxygen requirements of bacteria growing within.* Bacteria that require oxygen will grow close to the water s surface, and bacteria that cannot tolerate the presence of oxygen will grow at the bottom of the test tube.B GROWING BACTERIAL CULTURES ON SOUP MEDIA* Broth media can be made solid by adding agar, a gel like polysaccharide extracted from red algae.* Broth with about 1.5% agar added will be liquid when heated, but solid at room temperature, making it easy to pour into a vessel, such as a Petri dish or test tube when hot.* The solution then becomes solid once cooled.