Iron is left in the filter and salt solution (salt and water) passes into the cup.
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Explanation:
When a chlorine atom forms an ion, it gains electrons, making it negative. A neutral chlorine will become a chlorine with a -1 charge. When it gains an electron, the radius increases.
When a sodium atom forms an ion, it loses electrons, making it positive. A neutral sodium will become a sodium with a +1 charge. When it loses an electron, the radius decreases.