NDA GK Questions 2026

A vacuum contains no particles, and a mechanical wave such as sound can travel only by making particles vibrate and hand the disturbance on to their neighbours.

In a sound wave the particles of the medium vibrate back and forth along the same line in which the wave is travelling, producing regions where they crowd together, called compressions, and regions where they spread apart, called rarefactions.

The flash and the clap are produced at the same instant by the same discharge.

Amplitude is the maximum displacement of a particle of the medium from its rest position, and the energy carried by a wave increases with the square of the amplitude.

Convert the units first: 1 kilohertz is 1000 hertz and 50 centimetres is 0.5 metre. The speed is frequency multiplied by wavelength, that is 1000 multiplied by 0.5, which gives 500 metres per second.

Pitch is the characteristic of a sound by which the brain judges it as shrill or flat, and it is decided by the frequency of the wave.

The speed of a wave is the product of its frequency and its wavelength, so the speed here is 50 hertz multiplied by 4 metres, that is 200 metres per second.

The Minamata Convention on Mercury was adopted in 2013 and entered into force in 2017. It controls the supply and trade of mercury, restricts its use in products such as batteries, switches and certain measuring devices, and regulates emissions from coal burning and from small-scale gold mining.

The Cartagena Protocol on Biosafety, adopted in 2000, governs the safe handling, transport and use of living modified organisms produced by modern biotechnology.

The United Nations Conference on the Human Environment met at Stockholm in June 1972 and was the first global gathering to treat the environment as a subject of international policy.

The Basel Convention was adopted in 1989 after public anger at the export of toxic waste from industrialised countries to poorer ones, and it requires prior informed consent from the importing state before such a shipment may be made.

The Paris Agreement was adopted at the twenty-first Conference of the Parties in 2015 and entered into force in 2016.

The Kyoto Protocol was adopted at the third Conference of the Parties to the framework convention on climate change, held at Kyoto in Japan in 1997.

It was agreed at Washington in 1973 and came into force in 1975.

The Montreal Protocol was adopted in 1987 under the Vienna Convention of 1985 and entered into force in 1989. It fixed timetables for phasing out chlorofluorocarbons, halons, carbon tetrachloride and other ozone depleting chemicals, with later deadlines for developing countries.

The United Nations Conference on Environment and Development, popularly called the Earth Summit, met at Rio de Janeiro in 1992 and adopted Agenda 21, a detailed non-binding programme of action for sustainable development.

The Polar Code is the International Code for Ships Operating in Polar Waters, adopted by the International Maritime Organization and in force since the beginning of 2017.

The Ramsar Convention on Wetlands of International Importance was signed in 1971 in the Iranian city of Ramsar and came into force in 1975.

The Fourth Buddhist Council met in Kashmir under the patronage of the Kushana ruler Kanishka I. Vasumitra presided over it and Ashvaghosha acted as his deputy, and its work of collecting commentaries on the canon went with the open division of Buddhism into the Mahayana and Hinayana schools.

The Nasik cave inscription praising Gautamiputra Satakarni was issued in the name of his mother Gautami Balashri, in the reign of her grandson.