A hygrometer is an instrument used for measuring the moisture content in the atmosphere. Humidity measurement instruments usually rely on measurements of some other quantity such as temperature, pressure, mass or a mechanical or electrical change in a substance as moisture is absorbed.

Geothermal energy is the heat from the Earth. It's clean and sustainable. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth's surface and down even deeper to the extremely high temperatures of molten rock called magma. Hence option D is the right answer.

Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave.

Loudness is the characteristic of a sound that is primarily a psychological correlate of physical strength (amplitude).

Washing machine works on the principle of centrifugal force.

An electric motor is an electrical machine that converts electrical energy into mechanical energy. The reverse of this would be the conversion of mechanical energy into electrical energy and is done by an electric generator.

The SI unit of time is second, symbol is (σ).

A plane mirror is a mirror with a flat reflective surface. The focal length of a plane mirror is infinity. Its optical power is zero.

UV radiation is present in sunlight and is produced by electric arcs and specialized lights such as mercury-vapor lamps, tanning lamps, and black lights. Ozone layer blocks many UV frequencies from reaching telescopes on the surface of the Earth, most UV observations are made from space.

Bernoulli's principle can be derived from the principle of conservation of energy. This states that, in a steady flow, the sum of all forms of energy in a fluid along a streamline is the same at all points on that streamline.