Correct Answer: A

Rationale: The element with atomic number 26 and mass number 56 corresponds to Iron (Fe). Iron has 26 protons, which aligns with the given atomic number, and Fe-56 has 26 neutrons, which aligns with the given mass number. This confirms that Iron (Fe) is the correct answer. Cobalt (Co), Nickel (Ni), and Manganese (Mn) have different atomic numbers and mass numbers, so they are not the correct choices in this scenario.

Correct Answer: B

Rationale: An atom is the fundamental building block of matter, while molecules are formed by the combination of atoms.

Correct Answer: C

Rationale: The correct answer is an Electroencephalogram (EEG). An EEG is specifically designed to record the measurable electrical activity of the brain. It does so by using small, flat metal discs (electrodes) attached to the scalp to detect brain activity. This test is crucial in diagnosing various conditions like seizures, epilepsy, head injuries, dizziness, headaches, and brain tumors. The other options, CAT scan, MRI scan, and X-ray, are imaging techniques that do not directly measure the brain's electrical activity. CAT scan and MRI scan provide detailed images of the brain's structure, while X-ray is more suited for visualizing bone structures or dense tissues.

Correct Answer: A

Rationale: When sodium hydroxide (NaOH) reacts with hydrochloric acid (HCl), a neutralization reaction occurs. The products of this reaction are water (H2O) and a salt, which is sodium chloride (NaCl). The chemical equation for this reaction is: NaOH + HCl -> NaCl + H2O. Choice B is incorrect because chlorine gas and sodium oxide are not the products of this reaction. Choice C is incorrect as sodium metal and water are not the products formed in this neutralization reaction. Choice D is incorrect because a reaction does occur between NaOH and HCl, resulting in the formation of NaCl and H2O. Therefore, the correct answer is A: Hydrogen gas and sodium chloride (NaCl).

Correct Answer: A

Rationale: The correct answer is 'Atom.' An atom is the fundamental unit of an element that can exist independently and retain its unique chemical properties. It consists of a nucleus containing protons and neutrons, surrounded by electrons. Choice B, 'Molecule,' is incorrect because a molecule is a combination of two or more atoms bonded together. Choice C, 'Compound,' is incorrect as a compound is a substance formed by the chemical combination of two or more different elements. Choice D, 'Mixture,' is incorrect since a mixture is a blend of two or more substances physically combined, but the individual components retain their properties.