Practice MCQ Questions and answers on Chemistry-GK

A flame test is performed by introducing a sample into the blue flame of a bunsen burner and noting any change in the colour of the flame. The tests can be used to detect the presence of some metallic elements in salts. With strontium salt, the colour of Bunsen flame ranges from crimson to red.

An oxidising agent is an electron acceptor.

Silver gets corroded due to presence of Hydrogen sulphide in air.

Oxidation and chemical reaction with oxygen causes rusting of iron.

Oxidation is a process in which something (an atom or molecule or substance) loses an electron to something else. Photo-oxidation is therefore the process of oxidation which is caused by shining light on it. Often, light can be used to cause reactions to happen, such as oxidation. The term “photo” comes from “photon” which is light. The effect is facilitated by radiant energy such as UV or artificial light. This process is the most significant factor in weathering of polymers. Photo-oxidation is a chemical change that reduces the polymer’s molecular weight. As a consequence of this change the material becomes more brittle, with a reduction in its tensile, impact and elongation strength. Discolouration and loss of surface smoothness accompany photo-oxidation. High temperature and localized stress concentrations are factors that significantly increase the effect of photo-oxidation.

When copper is exposed to air, it reacts with moist carbon dioxide in the air and slowly loses its shiny brown surface and gains a green coat. This green substance is basic copper carbonate (CuCO₃. Cu (OH)₂). The formation of this green coating on the surface of a copper object corrodes it.

Foxing is a term describing the age-related spots and browning seen on vintage paper documents such as books, postage stamps, certificates, and so forth. It results from localized accelerated oxidation of cellulose or the effect on certain papers of the oxidation of iron, copper, etc.

A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the reaction itself. It achieves this by providing an alternative reaction pathway with a lower activation energy, which allows reactant molecules to more easily reach the transition state and form products.

Here's a breakdown of the options:
Option A: Increases the rate of the reaction: This option is correct. Catalysts are known for their ability to speed up chemical reactions, making them more efficient.
Option B: Decreases the rate of reaction: This statement is not correct. Catalysts do not slow down reactions; they accelerate them.
Option C: Has no action on the rate of the reaction: This statement is not correct. Catalysts specifically exist to increase the rate of chemical reactions.
Option D: None of these: This is not the correct option because Option A (Increases the rate of the reaction) is accurate.
Therefore, the correct answer is Option A: Increases the rate of the reaction.

The quick lime reaction with water is exothermic in nature due to production of heat. The slaked lime creates a suspension in water since it is only slightly soluble in water. The clear solution formed after the slaked lime gets settled is also known as lime water.

Oxygen has the highest percentage in both human body and on earth, but carbon, the element with the second highest percentage in the body, is relatively rare on Earth.