# GATE2020: 5

Determine the correctness or otherwise of the following Assertion [$a$] and the Reason [$r$] regarding mammalian cells.

Assertion [$a$]: Cells use $Ca^{2+}$, and not $Na^{+}$, for cell-to-cell signaling

Reason [$r$]: $n$ the cytosol, concentration of $Na^{+}$ is lower than that of $Ca^{2+}$

1. Both [$a$] and [$r$] are true and [r] is the correct reason for [$a$].
2. Both [$a$] and [$r$]  are true but [$r$] is not the correct reason for [$a$].
3. Both [$a$] and [$r$]  are false.
4. [$a$] is true but [$r$] is false.
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