RRB Group D GK Questions 2026

The Niagara river carries the water of Lake Erie to Lake Ontario, and on the way it crosses the Niagara escarpment, a band of hard dolomite, which produces the Horseshoe, American and Bridal Veil falls on the border of Canada and the United States.

The falls lie on the border of Zambia and Zimbabwe, where the Zambezi drops into a basalt gorge; the local name Mosi-oa-Tunya means the smoke that thunders, and the missionary explorer David Livingstone named them after Queen Victoria in 1855.

Angel Falls, called Salto Angel in Spanish, drops about 979 metres from the Auyan Tepui, one of the flat topped table mountains of the Guiana highlands, and is fed by the Churun river, a tributary of the Caroni.

It is a landlocked salt lake bordered by Russia, Kazakhstan, Turkmenistan, Iran and Azerbaijan, the remnant of the ancient Tethys sea, and is called a sea only by custom.

It lies in a rift valley in southern Siberia, reaches a depth of about 1,642 metres and holds more fresh water by volume than any other lake, roughly a fifth of the unfrozen surface fresh water of the earth.

A light year is the distance that light travels in vacuum in one year at about 3 into 10 to the power 8 metres per second, which works out to roughly 9.46 into 10 to the power 12 kilometres; astronomers use it because distances between stars are awkward to write…

Visible light runs from about 400 nanometres at the violet end to about 700 nanometres at the red end, so violet has the shortest wavelength, the highest frequency and the greatest energy of the seven colours remembered as VIBGYOR.

Maxwell showed that this speed is fixed by the electric permittivity and magnetic permeability of free space, and its agreement with the measured speed of light was the proof that light is an electromagnetic wave; every band of the spectrum shares the same value in vacuum.

Ozone in the stratosphere absorbs most of the harmful shorter ultraviolet, and that is why the thinning of the layer by chlorofluorocarbons raises the risk of skin cancer, cataract and damage to crops; the small part of ultraviolet that does reach the surface makes vitamin D in human skin.

A remote control carries a small light emitting diode that sends coded pulses of near infrared, which a sensor in the set decodes; the radiation is invisible, harmless at that power and does not pass through walls, so remotes in neighbouring rooms do not interfere.

In 1800 he passed sunlight through a prism and moved a thermometer across the coloured band; the reading went on rising past the red end, which showed the presence of an invisible heating radiation now called infrared.

In 1895 he noticed that a screen coated with a fluorescent salt glowed when a discharge tube was working nearby even though the tube was covered, and he called the unknown radiation X-rays; he received the first Nobel Prize in Physics in 1901 for the discovery.

The spectrum in order of rising wavelength runs gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves, and the option follows that sequence with the visible and microwave bands left out.

They have the shortest wavelength of the spectrum and therefore the highest frequency and energy, and being uncharged and very energetic they pass through several centimetres of lead, which is why thick shielding is needed in radiotherapy rooms.

Their wavelength runs from about a tenth of a metre up to many kilometres, which makes them the longest and therefore the lowest in frequency and energy of the whole spectrum; they are used in broadcasting, mobile telephony and radio astronomy.

In an electromagnetic wave the electric field, the magnetic field and the direction of propagation are mutually perpendicular, and because the wave is made of fields and not of vibrating particles it needs no medium, which is how sunlight crosses empty space while sound cannot.

In 1887 he used a spark gap oscillator to generate waves and a loop with a gap to detect them, and he measured their wavelength and showed that they behaved like light in reflection and refraction, which confirmed the theory.

Meristems are groups of actively dividing cells, and all new plant tissue comes from them. Meristematic cells are living, small and closely packed, with thin cellulose walls, dense cytoplasm, a large nucleus and few or no vacuoles.

The layers of graphite are held only by weak van der Waals forces, not by covalent bonds. Diamond and graphite are allotropes of carbon.

Soap lowers the surface tension of water, so water spreads into fine gaps and wets greasy dirt that plain water would bead up on.