50 NCLEX Fluid & Electrolyte Practice Questions (With Rationales)
Practice NCLEX-style fluid and electrolyte questions covering hyponatremia, hyperkalemia, dehydration, and fluid overload, with full rationales for every answer.
Fluid and electrolyte imbalances show up constantly on the NCLEX because they cross nearly every body system and every patient population. Mastering the classic sign/symptom clusters for each imbalance is one of the highest-yield things you can do this week. Below are sample questions in the same style as the full 50-question set in our high-yield bank.
Practice questions
1. A client has a serum potassium level of 6.2 mEq/L. Which finding should the nurse report immediately?
- A. Peaked T waves on the ECG
- B. Serum sodium of 140 mEq/L
- C. Respiratory rate of 18/min
- D. Mild muscle soreness
Show answer & rationale
Correct answer: A
Hyperkalemia causes peaked T waves, widened QRS complexes, and can progress to fatal dysrhythmias. This is the priority finding because it signals cardiac risk, not just a lab abnormality.
2. Which client is at greatest risk for hyponatremia?
- A. Client receiving IV normal saline post-op
- B. Client on SIADH-inducing medication drinking large amounts of water
- C. Client with diabetes insipidus
- D. Client with heat stroke and heavy sweating
Show answer & rationale
Correct answer: B
SIADH causes water retention that dilutes serum sodium; combined with excess free water intake, this is the classic setup for dilutional hyponatremia.
3. A client with heart failure develops fluid overload. Which assessment finding confirms this?
- A. Flat neck veins
- B. Bounding pulses and crackles on lung auscultation
- C. Dry mucous membranes
- D. Poor skin turgor
Show answer & rationale
Correct answer: B
Fluid volume excess presents with bounding pulses, adventitious lung sounds (crackles), jugular venous distention, and edema — the opposite of the dry, flat findings seen in dehydration.
4. Which lab value would the nurse expect in a client with severe vomiting and diarrhea for 3 days?
- A. Elevated BUN and hematocrit
- B. Decreased BUN
- C. Decreased hematocrit
- D. Normal urine specific gravity
Show answer & rationale
Correct answer: A
Fluid volume deficit hemoconcentrates the blood, raising both BUN and hematocrit; urine specific gravity also rises as the kidneys conserve water.
5. A client with hypocalcemia is at risk for which complication?
- A. Constipation
- B. Laryngospasm and tetany
- C. Hyporeflexia
- D. Hypertension
Show answer & rationale
Correct answer: B
Low calcium increases neuromuscular excitability, causing Chvostek's and Trousseau's signs, tetany, and potentially life-threatening laryngospasm.
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Work through the full NCLEX-RN question bank with detailed rationales for every answer.
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Frequently asked questions
What are the most tested electrolyte imbalances on the NCLEX?
Hyperkalemia, hyponatremia, hypocalcemia, and fluid volume excess/deficit appear most frequently because they have clear, testable sign/symptom clusters.
How should I memorize normal electrolyte ranges?
Anchor each electrolyte to one classic symptom cluster (e.g., high K+ = cardiac, low Ca2+ = neuromuscular) rather than memorizing numbers in isolation — NCLEX tests recognition, not recall of exact lab values.