The battery creates a across the electrodes. The positive terminal of the battery [pulls electrons away from/pushes electrons into] the electrode connected to it, charging the electrode [positively/negatively]. This attracts the [positively/negatively/neutrally] charged [sodium/chloride] ions in the brine. When these reach the electrode, the battery [pulls an electron away from/pushes electrons into] each of them. This converts them from [positively/negatively/neutrally] charged chloride ions into [positive/negative/neutral] chlorine atoms. These are unstable, so they bond covalently with one another in pairs, forming diatomic molecules of Cl2. This is what we often mean when we refer to chlorine. Chlorine is a dense green gas which bubbles away from this electrode and is collected. Chlorine was formed as chloride ions were stripped of electrons, so we call this half reaction [oxidation/reduction], which is the [gain/loss] of electrons. Each [chlorine atom/chloride ion] loses one electron to change it into a [chlorine atom/chloride ion]. The electrode at which oxidation occurs is called the [cathode/anode]. In an electrolytic cell, such as this, the battery charges the anode [positively/negatively].