To identify a physical change, we need to understand the fundamental difference between physical and chemical changes. A physical change alters the form or appearance of a substance but does not change its chemical composition. No new substances are formed. A chemical change (or chemical reaction) results in the formation of new substances with different chemical properties.
Correct Option: B) Melting of ice
A chemical reaction involves the rearrangement of atoms and molecules, leading to the formation of new substances. This process is often accompanied by observable changes, which serve as indicators that a reaction has taken place. We need to identify which of the given options is a common and reliable indicator of a chemical reaction.
Correct Option: C) Change in temperature
A change in temperature is a very common and significant indicator of a chemical reaction. Chemical reactions often involve the release of energy (exothermic reactions, leading to an increase in temperature) or the absorption of energy (endothermic reactions, leading to a decrease in temperature). For example, burning wood (combustion) releases heat, while dissolving certain salts in water can make the water feel colder.
The question asks to identify the product of the given chemical reaction. This is a single displacement reaction where a more reactive metal displaces hydrogen from an acid.
The given reaction is:
\[ \text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2 \]
In this reaction, Zinc (\(\text{Zn}\)) is a metal, and Sulfuric acid (\(\text{H}_2\text{SO}_4\)) is an acid.
Zinc is more reactive than hydrogen. Therefore, it displaces hydrogen from sulfuric acid.
When zinc displaces hydrogen, it combines with the sulfate radical (\(\text{SO}_4^{2-}\)) from the sulfuric acid to form a new compound.
The compound formed by the combination of Zinc (\(\text{Zn}^{2+}\)) and Sulfate (\(\text{SO}_4^{2-}\)) is Zinc Sulfate (\(\text{ZnSO}_4\)).
Hydrogen gas (\(\text{H}_2\)) is released as a byproduct.
Comparing the products in the reaction equation with the given options, \(\text{ZnSO}_4\) corresponds to Zinc sulphate.
Correct Option: C) Zinc sulphate
Which equation is balanced?
Hâ‚‚ + Oâ‚‚ → Hâ‚‚O
Fe + Hâ‚‚O → Fe₃Oâ‚„ + Hâ‚‚
Zn + HCl → ZnClâ‚‚ + Hâ‚‚
None of the Above
To determine which equation is balanced, we need to check if the number of atoms of each element on the reactant side (left side) is equal to the number of atoms of the same element on the product side (right side) for each given chemical equation. This is based on the Law of Conservation of Mass.
The given equation is:
\[ \text{H}_2 + \text{O}_2 \rightarrow \text{H}_2\text{O} \]Let's count the atoms:
Since the number of oxygen atoms is not equal (2 on reactant side, 1 on product side), this equation is not balanced.
The given equation is:
\[ \text{Fe} + \text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + \text{H}_2 \]Let's count the atoms:
Since the number of iron atoms (1 vs 3) and oxygen atoms (1 vs 4) are not equal, this equation is not balanced.
The given equation is:
\[ \text{Zn} + \text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \]Let's count the atoms:
Since the number of hydrogen atoms (1 vs 2) and chlorine atoms (1 vs 2) are not equal, this equation is not balanced.
D) None of the Above - As shown in the step-by-step analysis, all the provided chemical equations (A, B, and C) are unbalanced because the number of atoms of at least one element on the reactant side does not match the number of atoms of that element on the product side.
An exothermic reaction is a chemical reaction that releases energy, usually in the form of heat or light, to its surroundings. This results in a negative change in enthalpy (\(\Delta H < 0\)). Conversely, an endothermic reaction absorbs energy from its surroundings, resulting in a positive change in enthalpy (\(\Delta H > 0\)). We need to identify which of the given options releases energy.
C) Burning of methane is an exothermic reaction because it releases a significant amount of heat and light energy into the surroundings.
UPSC - 2022
The question asks about the primary role of B cells and T cells in the human body. This requires knowledge of the basic functions of the adaptive immune system.
Correct Option: D) They protect the body from the diseases caused by pathogens.
This statement accurately describes the primary function of B cells and T cells, which are central to the adaptive immune response against infectious agents like bacteria, viruses, fungi, and parasites.