Chemical Reactions

Step 1: Understanding the Question:
The question asks for the mechanism by which the ozone layer filters out dangerous solar radiation.

Step 2: Detailed Explanation:
In the stratosphere, ozone ((O_3)) molecules undergo a continuous cycle called the Chapman cycle.
When (O_3) is hit by high-energy Ultraviolet (UV) radiation from the sun, it absorbs the energy and breaks apart into an oxygen molecule ((O_2)) and a free oxygen atom (O).
[ O_3 + text{UV photon} rightarrow O_2 + O ] These components then recombine to form ozone again, releasing heat. This cycle effectively converts harmful UV energy into thermal energy before it can reach the Earth's surface.

Step 3: Final Answer:
Ozone protects the Earth through the cyclic process of splitting and recombining, which absorbs harmful UV radiation.

Step 1: Understanding the Question:
The question asks for a simple, observable way to distinguish between two clear, odorless solutions: sugar (sucrose) in water and salt (sodium chloride) in water.

Step 2: Detailed Explanation:
While multiple chemical tests exist, the most immediate "daily life" observation is biological.
Ants possess highly sensitive chemoreceptors for glucose and sucrose. If you pour both solutions on the floor, ants will be attracted to the sugar solution for its caloric content, whereas they will ignore the salt solution.
Option B is also technically true (sugar undergoes caramelization and then charring when heated dry), but option A is listed as the safest and most direct observational choice in the original context.

Step 3: Final Answer:
The presence of ants near the sugar solution is a reliable biological indicator to distinguish it from a salt solution.

Step 1: Understanding the Question:
The question asks for the biochemical reason behind the change in physical state of an egg yolk when it is cooked.

Step 2: Detailed Explanation:
Egg yolk is rich in proteins. In their natural state, these proteins are folded into specific 3D shapes.
When heat is applied, the kinetic energy breaks the weak bonds (like hydrogen bonds) holding the protein structure together. This process is called denaturation.
The uncoiled protein chains then bump into each other and form new, stronger bonds, creating a solid 3D network that traps water. This process is known as coagulation, which results in the solidification of the yolk.

Step 3: Final Answer:
Heating causes egg yolk proteins to denature and then coagulate into a solid mass.