Practice MCQ Questions and answers on Chemistry-GK

Petroleum is a complex mixture of hydrocarbons that occur in Earth in liquid, gaseous, or solid form.

A high-octane-rated fuel, such gasoline contains lead. Straight-run gasoline is distilled directly from crude oil. Once the leading source of fuel, its low octane rating required lead additives. Most countries have phased out leaded fuel. Different additives have replaced the lead compounds. The most popular additives include aromatic hydrocarbons, ethers and alcohol (usually ethanol or methanol). Lead used to be added to petrol and this was the source of high levels of lead in the air.

LPG is Liquefied Petroleum Gas and PNG is Piped Natural Gas. LPG is supplied in liquid form just as the name suggests in cylinders whereas PNG is supplied through a pipeline. LPG is used as a fuel in heating appliances and vehicles, where as PNG is used for cooking (gas stoves) and heating water (gas geysers).

Petroleum is a mixture of a very large number of different hydrocarbons; the most commonly found molecules are alkanes (paraffins), cycloalkanes (naphthenes), aromatic hydrocarbons, or more complicated chemicals like asphaltenes.

White coal is a form of fuel produced by drying chopped wood over a fire.

Paraffin wax is obtained from petroleum by dewaxing light lubricating oil stocks. It is used in candles, wax paper, polishes, cosmetics, and electrical insulators.

The hottest part of the gas flame is known as luminous zone.

As water is heavier than petrol therefore slips down permitting the petrol to rise to the surface and continue to burn. Besides, the existing temperature is so high that the water poured on the fire evaporates even before it can extinguisher the fire. Thus the petrol fire cannot be extinguished by water.

The oxy-acetylene flame is generated by burning acetylene (C₂H₂) in the presence of oxygen (O₂), creating one of the hottest known flame types used in industrial applications.

When acetylene combusts in oxygen, it undergoes a chemical reaction that releases a significant amount of heat:

C₂H₂ + 2.5O₂ → 2CO₂ + H₂O + Heat

This combustion produces a flame with two distinct zones: an inner cone and an outer envelope. The inner cone is the hottest part and is typically used for welding and cutting purposes.

The temperature of the inner cone in a neutral oxy-acetylene flame (balanced oxygen and acetylene) reaches approximately 3600°C (about 6530°F).

Such a high temperature is ideal for melting most metals, including steel and iron, which makes the flame extremely valuable in metalworking industries.

The flame can be adjusted to three types depending on the oxygen-to-acetylene ratio:

Neutral Flame: Equal oxygen and acetylene; used for welding most metals.

Carburizing (Reducing) Flame: Excess acetylene; used for specific applications like welding high-carbon steels.

Oxidizing Flame: Excess oxygen; used for cutting metals.

Among these, the neutral flame produces the highest and most efficient heat, reaching up to 3600°C.

Therefore, the correct answer is 3600°C (Option C).

Helium gas is lighter than air, therefore, a helium balloon rises, it is known as a noble gas and is therefore not reactive. Hydrogen is also lighter than air and even lighter than helium. However, Hydrogen is not used in balloons because it is highly explosive and flammable.