The elements in group 7 of the periodic table are known as the halogens - Edexcel - GCSE Chemistry - Question 6 - 2022 - Paper 1

Chlorine is more reactive than iodine due to the following reasons:

1. Atomic Structure: Chlorine has a smaller atomic radius compared to iodine. This means that the outer electrons in chlorine are closer to the nucleus, resulting in a stronger attraction between these electrons and the positive charge of the nucleus.

2. Electron Shel Shell: Chlorine has fewer electron shells than iodine, which means there is less electron shielding. This allows chlorine to gain an electron more readily, which is crucial for its reactivity as it readily forms compounds.

3. Electronegativity: Chlorine has a higher electronegativity compared to iodine, making it more effective in attracting electrons from other elements during chemical reactions.

The white crystals formed inside the gas jar after the reaction are sodium chloride (NaCl), commonly known as table salt.