➤ The ozone layer absorbs ultraviolet radiation, protecting living organisms from its harmful effects.
★ Ultraviolet radiation is harmful and causes skin damage, eye problems, and contributes to skin cancer.

➤ The correct formula for magnesium hydroxide is $\text{Mg(OH)}_2$, which is a common base.
★ Magnesium hydroxide is commonly used as an antacid and in wastewater treatment.

➤ When quick lime ($\text{CaO}$) reacts with water, it forms $\text{Ca(OH)}_2$, commonly known as slaked lime.
★ This reaction is highly exothermic and is used in various industrial processes.

➤ Au is the symbol for Gold, derived from the Latin word “aurum.”
★ Gold is a precious metal with a distinctive yellow color, highly valued in jewelry and electronics.

➤ Silicon is a metalloid, which exhibits properties of both metals and nonmetals.
★ Silicon is widely used in electronics and computer technology due to its semiconductor properties.

➤ When iron reacts with water, hydrogen gas is released.
★ This is a typical reaction for metals like iron in the presence of water and oxygen.

➤ He (Helium) is a noble gas, not a halogen.
★ Halogens include Fluorine (F), Chlorine (Cl), Bromine (Br), and Iodine (I).

➤ When zinc reacts with sulfuric acid, it forms zinc sulphate and hydrogen gas.
★ This reaction is an example of a single displacement reaction.

➤ When magnesium reacts with dilute sulfuric acid, hydrogen gas ($\text{H}_2$) is released.
★ This is a typical reaction between a metal and an acid, producing hydrogen gas.

➤ Helium is a monoatomic molecule because it exists as single atoms in its natural state.
★ Helium is a noble gas with a stable electron configuration, making it monoatomic.

➤ In a redox reaction, electrons are transferred between reactants—one is oxidized and the other is reduced.
★ Redox reactions are crucial in many biological and industrial processes, like respiration and combustion.

➤ When zinc reacts with sulfuric acid, hydrogen gas ($\text{H}_2$) is evolved.
★ This is a typical reaction where a metal displaces hydrogen from an acid, producing hydrogen gas.

➤ The dense mass of water drops mixed with smoke or dust is called smog, which is common in polluted areas.
★ Smog is harmful to health and reduces visibility, especially in urban environments.

➤ Curdling of milk is a chemical change, as it involves the formation of new substances (curd and whey).
★ Physical changes do not produce new substances, unlike chemical changes.

➤ Transition elements are found in the d-block of the periodic table.
★ These elements are characterized by their ability to form colored compounds and have variable oxidation states.

➤ The atomic radius is measured in picometres (pm), which is a very small unit of length.
★ Atomic radius is important in understanding the size of atoms and their behavior in chemical bonding.

➤ When the equation is balanced, there will be $2 \, \text{CO}_2$ and $3 \, \text{H}_2\text{O}$ molecules produced.
★ Balancing chemical equations ensures the conservation of mass and atoms.

➤ Sodium bicarbonate (baking soda) is used in fire extinguishers and to neutralize acids.
★ It is commonly used in households for baking, cleaning, and medical purposes.

➤ The straight chain alkane with the formula $\text{C}_9\text{H}_{20}$ is Nonane.
★ Nonane is used in organic synthesis and as a solvent in research.

➤ $\text{C}_3\text{H}_8$ (propane) is a saturated hydrocarbon (alkane) because it contains only single bonds between carbon atoms.
★ Saturated hydrocarbons follow the formula $\text{C}_n\text{H}_{2n+2}$ and are also called alkanes.

➤ Butyric acid ($\text{C}_4\text{H}_8\text{O}_2$) has the structure $\text{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$, making it a straight-chain carboxylic acid.
★ It has a foul smell and is found in rancid butter

➤ In a first order reaction, the reaction rate is proportional to the concentration of one reactant raised to the power one.
★ First order kinetics are common in radioactive decay and some chemical decompositions.

➤ Environmental water vapour does not enter the earthen pot through pores; instead, water inside oozes out and evaporates, causing cooling.
★ The cooling effect is due to evaporation, not absorption of moisture from the environment.

➤ Avogadro’s constant is $6.022 \times 10^{23}$, which defines the number of particles in one mole of a substance.
★ This constant is a fundamental concept in chemistry, helping to relate the macroscopic and microscopic worlds

➤ Nitric oxide (NO) is not considered a significant greenhouse gas, though it plays a role in atmospheric chemistry.
★ Greenhouse gases trap heat in the Earth’s atmosphere and include $\text{CO}_2$, $\text{CH}_4$, and $\text{N}_2\text{O}$.