Questions

The main group number for an element can be found from its column on the periodic table. For example, carbon is in group 4 and has 4 valence electrons. Oxygen is in group 6 and has 6 valence electrons.

Active voice is used when the subject performs the action stated by the verb.

Geothermal power plants are used in order to generate electricity by the use of geothermal energy (the Earth's internal thermal energy). They essentially work the same as a coal or nuclear power plant, the main difference being the heat source.

Geothermal power plants use hydrothermal resources that have both water (hydro) and heat (thermal). Geothermal power plants require high-temperature (300°F to 700°F) hydrothermal resources that come from either dry steam wells or from hot water wells.

Salivary glands of man are 3 pairs = 6. They are one pair of parotid glands, one pair of submaxillary or submandibular glands and one pair of sublingual glands.

Open market operations (OMO) refer to the buying and selling of government securities in the open market in order to expand or contract the amount of money in the banking system.

Dull means not sharp, not shining, not bright, ...

Hence, the given words are all that means the opposite of dull.