Final answer:
The nurse should report the digoxin level of 2.0 ng/mL as it may indicate potential digoxin toxicity. Other values, including potassium, serum creatinine, and sodium levels, are normal and don't need urgent reporting.
Step-by-step explanation:
The nurse should report option 3, which is a digoxin level of 2.0 ng/mL to the provider. This level may indicate digoxin toxicity, as the therapeutic range for digoxin is typically between 0.5 ng/mL and 2.0 ng/mL, with levels above this range potentially being harmful. The other options, including a normal potassium level of 4.2 mEq/L, serum creatinine within the normal range, and a normal sodium level of 140 mEq/L, are all within normal laboratory values and do not need to be reported as urgently.