Chemical Reactions — Set 1
Chemistry · रासायनिक अभिक्रियाएं · Questions 1–10 of 40
What type of chemical reaction occurs when two or more substances combine to form a single new substance?
Correct Answer: C. Combination reaction
A combination reaction involves multiple reactants joining to create one product. This process is also known as a synthesis reaction in many chemistry contexts. An example is the burning of magnesium in oxygen to form magnesium oxide.
Which of the following is an example of an exothermic reaction?
Correct Answer: C. Respiration
Respiration is an exothermic process because it releases energy for the body's use. It involves the breakdown of glucose in the presence of oxygen. Most combustion reactions are also classified as exothermic.
What is the term for a reaction where a more reactive element takes the place of a less reactive element in a compound?
Correct Answer: B. Displacement reaction
In a displacement reaction, a highly reactive metal replaces a lower reactivity metal from its salt solution. This follows the order of the reactivity series of metals. Iron reacting with copper sulfate is a classic example of this phenomenon.
In a redox reaction, what happens to the substance that undergoes reduction?
Correct Answer: D. It gains electrons
Reduction is defined as the gain of electrons by a chemical species. Conversely, oxidation involves the loss of electrons during the reaction. Both processes occur simultaneously in a single redox reaction.
What gas is evolved when a dilute acid reacts with a metal like Zinc?
Correct Answer: C. Hydrogen
Metals react with dilute acids to produce a salt and hydrogen gas. The presence of this gas can be tested using a burning matchstick which produces a pop sound. This is a common property of most active metals.
Which chemical is commonly used to test for the presence of Carbon Dioxide gas?
Correct Answer: D. Lime water
Lime water turns milky when carbon dioxide gas is passed through it. This occurs due to the formation of insoluble calcium carbonate precipitate. If the gas is passed in excess, the milkiness eventually disappears.
The process of food getting spoiled due to oxidation of fats and oils is called?
Correct Answer: A. Rancidity
Rancidity refers to the unpleasant smell and taste in food caused by fat oxidation. It can be prevented by adding antioxidants or using nitrogen gas in packaging. Storing food in airtight containers also slows down this process.
What color change is observed when Lead Nitrate powder is heated strongly?
Correct Answer: B. Turns yellow
Lead nitrate decomposes upon heating to form lead oxide, which is yellow in color. Brown fumes of nitrogen dioxide gas are also released during this reaction. This is a typical example of a thermal decomposition reaction.
Which of these is a physical change rather than a chemical reaction?
Correct Answer: D. Sublimation of camphor
Sublimation is a physical change because the chemical identity of the substance remains the same. The camphor simply changes from a solid state directly to a gaseous state. No new chemical bonds are broken or formed in this process.
What type of reaction occurs when an acid and a base react to form salt and water?
Correct Answer: A. Neutralization
Neutralization is the specific name for the reaction between an acid and a base. The H+ ions from the acid and OH- ions from the base combine to form water. This reaction is usually exothermic in nature.