Engineering Entrance ( Science )

A thermo-electric pyrometer is designed to measure very high temperatures, such as those in furnaces, where standard thermometers would fail.

When a balloon bursts, the stored elastic potential energy converts to kinetic energy of the rubber fragments and air. The total kinetic energy increases as potential energy decreases, conserving total energy.

Mercury is preferred because its high density allows for a much shorter tube compared to water, and its low vapour pressure prevents it from evaporating into the vacuum space.

When the girl stands up, the center of gravity of the swing system rises, effectively shortening the length of the pendulum (L). Since the time period T = 2 * pi * sqrt(L/g), a decrease in L results in a decrease in the time period.

Animal charcoal is produced by the destructive distillation of bones in the absence of air, which leaves behind a carbon-rich residue.

Potassium permanganate (KMnO4) is a dark-purple crystalline solid that acts as a strong oxidizing agent, making it effective as an antiseptic and disinfectant.

In coordination complexes, the central metal atom/ion exhibits primary valency (oxidation state) satisfied by anions and secondary valency (coordination number) satisfied by ligands (donor molecules). Since all these properties are characteristic of metal complexes, 'all of these' is correct.

Nitrogen is produced in the laboratory by heating ammonium chloride (NH4Cl) with sodium nitrite (NaNO2), producing NaCl, N2, and H2O. This is a standard nitrogen preparation method. Option B has a typo (nitrarte), and options C and D don't produce nitrogen gas.

Photographic plates and films are coated with a light-sensitive emulsion containing silver bromide, which decomposes upon exposure to light.

Saponification is the chemical reaction between a fat (triglyceride) and a strong alkali (like NaOH or KOH) to produce glycerol and soap.

On a large industrial scale, oxygen is primarily obtained through the fractional distillation of liquid air, but among the choices, water electrolysis is the standard method for producing high-purity oxygen.

Distillation is an effective method for purifying metals with low boiling points, such as mercury (Hg) and zinc (Zn), as they can be vaporized and condensed away from non-volatile impurities.

 Temporary hardness is due to the presence of calcium hydrogencarbonate Ca(HCO₃)₂(aq) and magnesium hydrogencarbonate Mg(HCO₃)₂(aq). Both calcium hydrogencarbonate and magnesium hydrogencarbonate decompose when heated. The original insoluble carbonate is reformed. This happens when water is boiled. The precipitation reactions are as follows:   

Oxidative refining (or cupellation/puddling) is used to remove impurities like carbon and silicon from iron by oxidizing them into gases or slag.

The only non-metal that is a liquid at room temperature and normal pressure is a halogen called bromine.

A compound is a substance formed when two or more elements are chemically bonded together in a fixed ratio. Water (H2O) fits this definition.

Lead pencils do not contain the element lead; they contain a mixture of graphite and clay. Graphite is the material that leaves marks on paper.

Stainless steel is primarily an alloy of iron, chromium, and nickel. Chromium is added to provide corrosion resistance, while nickel improves the mechanical properties and corrosion resistance further.

Calomel is also called mercurous chloride (Hg₂Cl₂) or mercury(I) chloride.

Waterproof fabrics often rely on the hydrophobic nature of their coating, which increases the contact angle of water droplets. This phenomenon is governed by surface tension, preventing water from penetrating the pores of the material.