As the elements in group 17 are considered in order of increasing atomic number, the chemical reactivity of each successive element
(1) decreases
(2) increases
(3) remains the same

Summarized

chemical and physical properties of  the reactants are changed. iron (fe) shiny , silver solid that mostly reacts with oxygen (o2)  a colorless, odorless gas to form an iron oxide a brown orange solid. chemical change involved in the rusting of iron is clearly color change.common observations that occur during a chemical reaction include the formation of gas,the information of solid,the dissapperance of solid, absorption or release of heat. not all chemical actions are easily observed. ex. reaction between aqueous solution of naOH and aqueous HCI results of the information of an aqueous solution of NaCI. all solution are colorless liquids, so it is not obvious that chemical reaction is taking place, and the use of analytical instruments . the ability to predict when a reaction should occur becomes important in these instances

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