<b>Concept:</b> Electric field can be expressed in two equivalent units.<br><br><b>Definition 1:</b> Force per unit charge<br>E = F/q<br>Unit = Newton/Coulomb = <b>N/C</b><br><br><b>Definition 2:</b> Negative gradient of potential<br>E = -dV/dx<br>Unit = Volt/metre = <b>V/m</b><br><br><b>Verification of equivalence:</b><br>1 V/m = 1 (J/C)/m = 1 J/(C·m) = 1 (N·m)/(C·m) = 1 N/C ✓<br><br><b>Both N/C and V/m are valid SI units of electric field.</b><br><br><b>Answer:</b> Option (C) Both (a) and (b)