Question

which ion tends to move into a living cell due to both its concentration gradient and electrical gradient?
a.) sodium (na⁺)
b.) chloride (cl⁻)
c.) potassium (k⁺)
d.) calcium (ca2⁺)

Explanation:

Sodium ions ($Na^+$) have a higher concentration outside the cell compared to inside (concentration gradient favoring entry). Also, the inside of the cell is relatively negative (electrical gradient, as the resting membrane potential is around -70 mV in many cells) and $Na^+$ is positively charged, so the electrical gradient also favors $Na^+$ moving into the cell. Chloride ($Cl^-$) has a different distribution and electrical - concentration gradient balance. Potassium ($K^+$) has a higher concentration inside the cell (concentration gradient usually favors exit). Calcium ($Ca^{2+}$) has a very low intracellular concentration, but its movement is more regulated and not as straightforwardly driven by both gradients in the same simple "always - in" direction as $Na^+$ in many basic cell scenarios.

Answer:

A. Sodium ($Na^+$)