Chemistry

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Which type of RNA is used to carry the genetic code copied from DNA?

  • A. mRNA
  • B. tRNA
  • C. rRNA
  • D. None of the above
Correct Answer: A

Rationale: The correct answer is mRNA (messenger RNA). mRNA is responsible for carrying the genetic information copied from DNA in the cell nucleus to the ribosomes in the cytoplasm where protein synthesis occurs. This process is known as transcription. mRNA acts as a messenger, delivering the genetic instructions to the ribosomes for protein synthesis. In contrast, tRNA (transfer RNA) brings specific amino acids to the ribosome during translation, helping to assemble the protein chain. rRNA (ribosomal RNA) forms a structural and catalytic part of the ribosome itself, aiding in protein synthesis. Therefore, among the options provided, mRNA is the RNA type directly involved in carrying the genetic code from DNA for protein production.

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A block on your desk acts as a paperweight with measurements of 3 cm by 4 cm by 6 cm. The block has a mass of 184.32 g. What is its density?

  • A. 13,271.04 g/cm³
  • B. 2.56 g/cm³
  • C. 0.39 g/cm³
  • D. None of the above
Correct Answer: B

Rationale: Density is calculated by dividing mass by volume. To find the volume of the block, multiply its dimensions (3 cm x 4 cm x 6 cm = 72 cm³). Dividing the mass (184.32 g) by the volume (72 cm³) gives a density of 2.56 g/cm³. Therefore, the correct answer is B.

Which subatomic particle can always be used to identify an atom?

  • A. Protons
  • B. Neutrons
  • C. Electrons
  • D. None of the above
Correct Answer: A

Rationale: The correct answer is A: Protons. Protons are positively charged subatomic particles found in the nucleus of an atom. The number of protons in an atom's nucleus determines the element's identity. While neutrons and electrons are also essential components of an atom, it is the number of protons that uniquely identifies the element. Therefore, protons can always be used to identify an atom.

Which of the following must be present in order to be considered an organic molecule?

  • A. H
  • B. O
  • C. N
  • D. C
Correct Answer: D

Rationale: To be considered an organic molecule, carbon (C) must be present. Organic molecules are primarily composed of carbon atoms bonded to hydrogen (H) atoms, along with other elements like oxygen (O), nitrogen (N), sulfur, and phosphorus. Carbon is the backbone of organic compounds due to its unique bonding properties and ability to form long and complex chains, making it an essential element in organic chemistry. While hydrogen, oxygen, and nitrogen are commonly found in organic molecules, it is the presence of carbon that defines a compound as organic. Without carbon, a molecule cannot be classified as organic, regardless of the presence of other elements.

Arrange the following unknown fluids in the correct order of how they would separate in a beaker, listed from bottom to top, based on the given measurements.

  • A. A, B, C
  • B. A, C, B
  • C. C, A, B
  • D. B, A, C
Correct Answer: B

Rationale: To determine the order of separation in a beaker, we need to consider the densities of the fluids. Density (d) = mass (m) / volume (V). Comparing the densities of the fluids, we find: Fluid A: d = 2060g / 2000mL = 1.03 g/mL, Fluid B: d = 672g / 850mL = 0.79 g/mL, Fluid C: d = 990g / 1100mL = 0.90 g/mL. Since fluids separate in a beaker based on their densities (with the highest density sinking to the bottom), the correct order from bottom to top is B (highest density), then C, and finally A (lowest density). Therefore, the correct answer is A,C,B.

Which type of bond involves atoms gaining or losing electrons?

  • A. Ionic
  • B. Covalent
  • C. Both
  • D. Neither
Correct Answer: A

Rationale: Ionic bonds involve the transfer of electrons between atoms, leading to one atom gaining electrons (becoming negatively charged) while the other loses electrons (becoming positively charged). This results in the formation of ions that are held together by electrostatic forces, creating an ionic bond. In a covalent bond, atoms share electrons rather than gaining or losing them, making option A, 'Ionic,' the correct answer to this question. Therefore, the correct answer is 'Ionic,' as it specifically involves gaining or losing electrons to form a bond.

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