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Which of the following is a characteristic of an exothermic reaction?
- A. It absorbs heat
- B. It releases heat
- C. It remains neutral
- D. It requires energy input
Correct Answer: B
Rationale: An exothermic reaction is characterized by the release of heat. During an exothermic reaction, energy is released in the form of heat to the surroundings, resulting in a temperature increase. This distinguishes it from endothermic reactions, which absorb heat from the surroundings. Choice A is incorrect because exothermic reactions do not absorb heat; instead, they release heat. Choice C is incorrect as exothermic reactions do not remain neutral; they involve a net release of energy. Choice D is incorrect as exothermic reactions do not require energy input; instead, they release energy.
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What type of bond is present in sodium chloride?
- A. Covalent
- B. Ionic
- C. Metallic
- D. Hydrogen
Correct Answer: B
Rationale: Ionic bonds are found in sodium chloride. In an ionic bond, one atom donates an electron to another atom, resulting in the formation of positively and negatively charged ions that are held together by electrostatic forces of attraction. Sodium chloride is a classic example of an ionic compound, where sodium (Na) donates an electron to chlorine (Cl), forming Na+ and Cl- ions that are attracted to each other, creating a crystal lattice structure. Covalent bonds involve the sharing of electron pairs between atoms, which is not the case in sodium chloride. Metallic bonds occur in metals where electrons are delocalized and shared across a lattice, unlike the specific transfer seen in ionic bonds. Hydrogen bonds are a type of intermolecular force, not the primary bond type present in sodium chloride.
What is the name of the bond formed when two atoms share electrons?
- A. Covalent bond
- B. Ionic bond
- C. Metallic bond
- D. Hydrogen bond
Correct Answer: A
Rationale: A covalent bond is formed when two atoms share electrons, creating a stable electron configuration. This sharing allows both atoms to achieve a full outer shell of electrons, leading to a stable molecule. In contrast, an ionic bond involves the transfer of electrons from one atom to another, resulting in the formation of ions with opposite charges. Metallic bonds are formed between metal atoms and involve a 'sea of electrons' that are delocalized and free to move. Hydrogen bonds are a type of intermolecular force, not a true chemical bond, and occur between a hydrogen atom and a highly electronegative atom like oxygen or nitrogen.
What is the chemical symbol for sodium?
- A. N
- B. Na
- C. Cl
- D. H
Correct Answer: B
Rationale: The correct chemical symbol for sodium is 'Na.' In the periodic table, sodium is represented by the symbol 'Na,' derived from its Latin name 'natrium.' The symbol 'N' represents nitrogen, not sodium. 'Cl' is the symbol for chlorine, and 'H' is the symbol for hydrogen. Therefore, 'Na' is the correct chemical symbol for sodium.
Which of the following best describes an endothermic reaction?
- A. A reaction that absorbs heat
- B. A reaction that releases heat
- C. A reaction that does not involve heat
- D. A reaction that remains at a constant temperature
Correct Answer: A
Rationale: An endothermic reaction is a process that absorbs heat from its surroundings. When a reaction absorbs heat, it leads to a decrease in the temperature of the surroundings, making choice A the correct description. In an endothermic reaction, energy is taken in from the surroundings, resulting in a decrease in temperature around the reaction site. Choice B is incorrect because a reaction that releases heat is known as an exothermic reaction. Choice C is incorrect as all reactions involve heat to some extent. Choice D is incorrect as an endothermic reaction does not remain at a constant temperature but rather absorbs heat, leading to a temperature decrease in the surroundings.
Which element has the chemical symbol 'Fe'?
- A. Lead
- B. Iron
- C. Silver
- D. Copper
Correct Answer: B
Rationale: The correct answer is 'Iron' as it has the chemical symbol 'Fe'. Chemical symbols are used to represent elements in the periodic table, and 'Fe' specifically refers to Iron. Choice A, Lead, is incorrect as the chemical symbol for Lead is 'Pb'. Choice C, Silver, is incorrect as the chemical symbol for Silver is 'Ag'. Choice D, Copper, is incorrect as the chemical symbol for Copper is 'Cu'. Therefore, 'Iron' is the only element among the choices with the chemical symbol 'Fe'.