Chemistry MCQs

Notes:
Silver is the metal with the highest electrical and thermal conductivity. It has only one valence electron, which can move around with little resistance. This makes silver a great conductor of electricity and heat.
Silver’s thermal conductivity is 430 wK/m, which is higher than copper (400 wK/m), aluminum (235 wK/m), and brass (109 wK/m).
Silver’s low contact wear resistance and excellent optical reflectivity make it ideal for coating contacts, mirrors, and conductors in telecom applications.
Impurities can decrease a conductor’s conductivity. For example, sterling silver is not as good of a conductor as pure silver. Oxidized silver is not as good a conductor as untarnished silver.

Notes:
Barium Sulphate is the correct answer. It is used as a radiopaque contrast agent in X-ray imaging because it absorbs X-rays, making it visible on the images. Commonly referred to as “Barium Meal” when ingested for gastrointestinal studies, it helps diagnose conditions like ulcers and tumors. Barium Sulphate is insoluble in water, ensuring it remains in the digestive tract without being absorbed.

Notes:
The auto-ignition temperature of a liquid, gas or vapor is the temperature at which the substance will ignite without any external heat source. Here is the temperature of some gases: 
Methane -580 °C 
Hydrogen -560 °C 
Propane -493 °C 
Ethylene -425 °C 
Acetylene -305 °C 
Naphtha -290 °C 
Carbon disulfide -102 °C

Notes:
Acid rain, or acid deposition, is a broad term that includes any form of precipitation with acidic components, such as sulphuric or nitric acid that fall to the ground from the atmosphere in wet or dry forms.

Notes:
(i) It is an important primary material for manufacturing cement and is the cheapest form of alkali. (ii) It is used in the manufacture of sodium carbonate from caustic soda. (iii) It is employed in the purification of sugar and in the manufacture of dye stuffs.

Notes:
Of the alkaline earth metals calcium and magnesium rank fifth and sixth in abundance respectively in the earth’s crust. Strontium and barium have much lower abundances. Beryllium is rare and radium is the rarest of all comprising only 10^–10 per cent of igneous rocks.

Notes:
Fractional distillation method is used to separate a mixture of two or more miscible liquids for which the difference in boiling points is less than 25 K. example: Air, crude oil, chlorosilanes etc.

Notes:
Sphalerite (ZnS) is a sulphide. All others are oxides. Haematite and Magnetite are the oxides of iron and Cuprite is an oxide of Copper.

Notes:
Corundum is an ore of Aluminium. It is a crystalline form of aluminium oxide. Kieserite is an ore of Magnesium and Pitch blende is an ore of Uranium.

Notes:
The probability of finding an electron at a point within an atom is proportional to the square of the orbital wave function i.e., ψ|² at that point. |ψ|² is known as probability density and is always positive.