Chemistry MCQs

Notes:
Bakelite is a thermosetting plastic formed from phenol and formaldehyde, used in electrical insulators and cookware handles. Unlike thermoplastics, it hardens irreversibly when heated and cannot be remolded. It was the first synthetic plastic, invented by Leo Baekeland in 1907.

Notes:
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature.

Notes:
The bright red color in fireworks is due to the presence of Strontium salts. The Strontium atom, upon yielding its energy in a quick burst upon heating, emits a brilliant red light. In fact, such properties of elements are used to identify them in a flame test, a classic method in chemistry labs across the globe.

Notes:
A molecule represents the smallest portion of a substance that retains the characteristics of the substance. It’s electrically neutral because it’s made up of atoms that bond together, sharing or exchanging electrons to achieve stability. This process balances out the electrical charges of the protons and electrons, rendering the molecule as a whole electrically neutral.

Notes:
Allotropes refer to two or more different physical forms in which an element can exist. The property is due to different ways atoms bond together. The most common instance is the element carbon, which exists in several different forms, including diamond, graphite, and fullerenes, making it an allotropic element. It’s crucial to note that allotropy applies to elements, not compounds.

Notes:
One important character of Ionic solids is that they readily get dissolved in water

Notes:
The auto-ignition temperature of a liquid, gas or vapor is the temperature at which the substance will ignite without any external heat source. Here is the temperature of some gases: 
Methane -580 °C 
Hydrogen -560 °C 
Propane -493 °C 
Ethylene -425 °C 
Acetylene -305 °C 
Naphtha -290 °C 
Carbon disulfide -102 °C

Notes:
Iodine-135 is a important by-product of nuclear fission, particularly in reactors using uranium fuel. It has a high neutron capture cross-section, meaning it effectively absorbs neutrons, which can inhibit the fission process and reduce reactor power output. This property makes it crucial for managing reactor control and safety, as its presence can lead to a phenomenon known as “neutron poison,” affecting the overall efficiency of the nuclear reaction.

Notes:
The correct answer is Mercury. An amalgam is a specific type of alloy that primarily consists of mercury mixed with another metal, commonly used in dental fillings due to its durability and ease of use. Historically, amalgams have been used since ancient times, with the earliest known use dating back to the 9th century in China.

Notes:
Sublimation is the process where a solid turns directly into a gas without passing through the liquid phase.

• Iodine: Sublimes at about 113.7°C, releasing purple vapors.
• Naphthalene: Sublimes at around 80°C, commonly used in mothballs.
• Camphor: Sublimes at approximately 175°C, used in medicinal and aromatic applications.

All three substances can undergo sublimation upon heating, making the correct answer “All of them.”