Which two elements react together to form an ionic compound?

Correct Answer: C

Rationale: The correct answer is C, X and Z. Ionic compounds are formed when a metal (X) reacts with a nonmetal (Z) by transferring electrons to achieve a stable octet configuration. Metal atoms tend to lose electrons to form positively charged cations, while nonmetal atoms tend to gain electrons to form negatively charged anions. In this case, X (metal) and Z (nonmetal) will react to form an ionic compound through electron transfer. Choices A, B, and D are incorrect because they do not involve a metal-nonmetal combination, which is essential for the formation of an ionic compound.

Correct Answer: B

Rationale: The correct answer is B because steroid hormones bind to DNA and form a gene-hormone complex, which then regulates gene expression. This directly influences cellular activities at the genetic level. Choices A, C, and D are incorrect because steroid hormones do not activate cyclic AMP, G proteins, or use calcium ions as second messengers for their cellular actions. Steroid hormones act through genomic mechanisms, not via the signaling pathways associated with choices A, C, and D.

Correct Answer: A

Rationale: The correct answer is A because the binding of a steroid hormone to its receptor triggers a series of events that ultimately lead to the transcription of DNA for the gene that is 'turned on'. This process involves the hormone-receptor complex entering the nucleus, binding to specific DNA sequences, recruiting transcription factors, and initiating gene expression. Choice B is incorrect because steroid hormones do not typically use second messengers for signaling. Choice C is incorrect because while some hormones can activate enzymes indirectly, steroid hormones primarily act through gene transcription. Choice D is incorrect because cAMP is typically associated with signaling pathways involving non-steroid hormones like adrenaline.

Correct Answer: C

Rationale: Rationale: The isthmus of the thyroid gland is located between the 2nd and 3rd tracheal rings. These rings provide support to the trachea and help maintain its shape. Therefore, the correct answer is C. Summary of other choices: A: 1st and 2nd - Incorrect, as the isthmus is not related to the 1st tracheal ring. B: 1st, 2nd and 3rd - Incorrect, as the isthmus is only between the 2nd and 3rd tracheal rings. D: 2nd, 3rd and 4th - Incorrect, as the isthmus does not extend to the 4th tracheal ring.

Correct Answer: C

Rationale: The correct answer is C: Pretracheal fascia. This layer surrounds the thyroid gland, forming the false capsule. It separates the thyroid from the strap muscles anteriorly and the trachea and esophagus posteriorly. The Carotid sheath (A) encloses the common carotid artery, internal jugular vein, and vagus nerve. The Investing layer (B) covers the sternocleidomastoid and trapezius muscles. The Prevertebral fascia (D) surrounds the vertebral column and deep neck muscles, not directly related to the thyroid gland.