Chemistry MCQs

Notes:
The carat is the common unit used to describe the mass of a gem. A 1-carat diamond, for example, has a mass of 0.20 g. The karat is the common unit used to describe the purity of a precious metal, such as gold. A 24-karat gold ring is as pure as can be. A gold ring that is 50 % pure is 12 karat.

Notes:
The oxidizing power of elements increases on moving left to right along a period in the periodic table. This is because electronegativity and the non-metallic character increases from left to right.

Notes:
Graphite is renowned for its conspicuous uses owing to its unique properties like its ability to conduct electricity, which makes it ideal for electrode manufacturing. It’s also used as a lubricant and in the production of crucibles, thanks to its high melting point. However, it isn’t used in glass cutting.

Notes:
Electronegativity is defined as an atom’s ability to attract an electron pair when forming a covalent bond. This property increases as you move left to right across the periodic table due to an increase in the nuclear charge’s attractive forces. It decreases as you move top to bottom, owing to the shielding effect of sub-levels and increased atomic radius, which makes electrons easier to remove. This culminates in Fluorine, being the highest and furthest to the right on the periodic table, hence it is the most electronegative.

Notes:
Froth and foams are examples of “gas suspended in liquid”. They are typically created when gas bubbles are dispersed in a liquid. This physical phenomenon is commonly observed in many daily life scenarios such as soap lather and carbonated drinks. Technically, they are a special case of colloid where little blobs of one liquid are dispersed in another and show the property of surface tension.

Notes:
The correct answer is 2. The lanthanides are a series of 15 elements in the periodic table, from atomic numbers 57 (Lanthanum) to 71 (Lutetium). They are known for their similar properties and are often found together in nature. The range of atomic numbers for lanthanides is 57 to 71, not 57-70 or 58-70.

Notes:
In 17 carat gold, the composition is 17 parts gold and 7 parts other metals, making it 70.6% gold. The term “carat” refers to the purity of gold, with 24 carats being pure gold. Thus, 17 carat gold contains 7 parts of other metals, which can include copper, silver, or palladium, used to enhance durability and alter color.

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:
Carbamide is another name of Urea, an organic compound with chemical formula CO(NH₂)₂. This name indicates that Urea is an amide in which two –NH₂ groups are joined by a carbonyl (C=O) functional group.

Notes:
Pyrolusite, Braunite, Psilomelane, and Rhodochrosite are all ores of Manganese. Pyrolusite is one of the most important ores due to its high manganese content. Braunite, although a significant ore, its manganese content is less than Pyrolusite. Psilomelane and Rhodochrosite also contribute as minor ores.