Chemistry - Study Mode

[#306] Which is the highest quality of hard coal?
Correct Answer

(A) Anthracite

Explanation

Solution: Anthracite, often referred to as hard coal, is a hard, compact variety of coal that has a submetallic luster. It has the highest carbon content, the fewest impurities, and the highest energy density of all types of coal and is the highest ranking of coals.

[#307] The main source of Naphthalene is
Correct Answer

(C) Coal-tar

Explanation

Solution: Most naphthalene is derived from coal tar. From the 1960s until the 1990s, significant amounts of naphthalene were also produced from heavy petroleum fractions during petroleum refining, but today petroleum-derived naphthalene represents only a minor component of naphthalene production.

[#308] The addition of gypsum to portland cement helps in :
Correct Answer

(C) Preventing rapid setting of cement

Explanation

Solution: Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates, the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO 2 shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed 5.0% by mass. Cement sets when mixed with water by way of a complex series of chemical reactions still only partly understood. The different constituents slowly crystallise and the interlocking of their crystals gives cement its strength. Carbon dioxide is slowly absorbed to convert the portlandite (Ca(OH) 2 ) into insoluble calcium carbonate. After the initial setting, immersion in warm water will speed up setting. Gypsum is added as an inhibitor to prevent flash setting.

[#309] Which gas is most stable at room temperature?
Correct Answer

(B) N 2

Explanation

Solution: Nitrogen (N 2 ) is most stable at room temperature.

[#310] Which of the following is used as a preservative to protect processed food?
Correct Answer

(D) Sodium metabisulphite

Explanation

Solution: Sodium metabisulphite is used as a preservative to protect processed food.