Chlorine, bromine and iodine belong to the same group and

Analyze the question: Chlorine, bromine and iodine are Group 17 elements (the halogens). We need the statement that is true of all three.

Concept: Elements in the same group share similar chemical properties because they have the same number of valence electrons (7). They differ in physical properties, and their reactivity decreases down the group.

Check each option:

• A. Gaseous at room temperature: False. Chlorine is a gas, bromine is a liquid, and iodine is a solid.
• B. White precipitate with AgNO₃(aq): False for the elements themselves. The halide ions give precipitates, and only AgCl is white. AgBr is cream/pale yellow and AgI is yellow.
• C. React violently with hydrogen without heating: False. Only fluorine reacts explosively with hydrogen in the dark. Chlorine needs sunlight or heat, and bromine and iodine need heating (iodine's reaction is also reversible and slow).
• D. React with alkali: True. All halogens react with alkalis such as NaOH: • Cold, dilute alkali: Cl₂ + 2NaOH → NaCl + NaOCl + H₂O • Hot, concentrated alkali: 3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O • Bromine and iodine behave similarly, forming halides and hypohalites or halates.

Answer: D.

Tip: For "same group" questions, look for a chemical property shared by all members (such as reacting with alkali). Physical states and the colors of precipitates vary down the group. Remember the silver halide colors as white, cream, yellow for Cl, Br, I.