The atomic number of carbon is 6. How many unpaired electrons are in its outer shell?
Two
Three
Four
Five
The Correct Answer is A
A. Two: Carbon has the electron configuration 1s² 2s² 2p². In the outer shell (n = 2), the two electrons in the 2p orbitals occupy separate orbitals according to Hund’s rule, resulting in two unpaired electrons. These unpaired electrons explain carbon’s ability to form four covalent bonds.
B. Three: Having three unpaired electrons would require three singly occupied p orbitals, which does not occur in carbon’s ground-state configuration. Carbon has only two electrons in the 2p subshell, not three. This option does not align with orbital filling rules.
C. Four: Although carbon has four valence electrons, not all are unpaired. The two electrons in the 2s orbital are paired, leaving only the 2p electrons unpaired. Valence electron count is not the same as unpaired electron count.
D. Five: Carbon does not have five electrons in its outer shell, nor does it have enough orbitals to support five unpaired electrons. This number exceeds the maximum possible valence electrons for a second-period element.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. Integrating sensory information: The CNS, composed of the brain and spinal cord, receives and integrates sensory input from the peripheral nervous system. This process allows the CNS to interpret stimuli from both internal and external environments and coordinate appropriate responses.
B. Evaluating the information: The CNS evaluates sensory data by analyzing, comparing, and interpreting it in relation to past experiences and current conditions. This cognitive processing is essential for decision-making, perception, and planning of actions.
C. Initiating an outgoing response: After processing sensory information, the CNS generates motor commands that are sent through the peripheral nervous system to muscles or glands. This enables coordinated voluntary and involuntary responses to stimuli.
D. All of the above are functions of the CNS: Integration, evaluation, and initiation of responses are all core functions of the CNS. Together, they allow the central nervous system to serve as the control center of the body, coordinating perception, cognition, and action.
Correct Answer is D
Explanation
A. Ureters: The ureters are paired fibromuscular tubes, that originate from the renal pelvis of each kidney. Their walls contain smooth muscle layers (longitudinal and circular) that generate peristaltic waves to propel urine toward the urinary bladder. Their structural role in urine transport classifies them as accessory organs.
B. Urinary bladder: The urinary bladder is a hollow, distensible muscular organ located in the pelvic cavity, posterior to the pubic symphysis. It allows for storage of variable urine volumes. The bladder receives ureters at the trigone, a triangular anatomical area that ensures one-way urine flow, and connects inferiorly to the urethra.
C. Urethra: The urethra is a fibromuscular canal that conducts urine from the bladder to the external urethral orifice. Its wall contains smooth muscle and mucosal folds, facilitating controlled voluntary and involuntary urine passage. Its anatomical design as a conduit makes it an accessory structure of the urinary system.
D. All of the above: Collectively, the ureters, urinary bladder, and urethra do not participate in urine formation but are structurally and functionally essential for urine transport, storage, and excretion. Each possesses distinct anatomical features as accessory organs of the urinary system.
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