Which ones of this are an oxidation-reduction reaction? and why?
(A) Hcl (aq) → H+(aq) + cl-(aq) (B) CH4 + cl2 → CH3cl + Hcl
(C) 2 CrO4 2-+ 2H+ → Cr2O72-+ H2O (D) Zn + Hcl → Zncl 2 + H2

pure substance: iron,copper

impure substance: water,charcoal

its first and third is your answer i did the qustion the fourth isnt right

answer:

the reaction is type of combination reaction.

explanation:

on the product side, there are 2 molecules of bonded to fe   which means one atom of fe are combined two molecules of . so, balanced chemical equation becomes :

this reaction follows the reaction type of combination reaction. a combination reaction is defined as chemical reaction in which reactants combines together to form a single product.

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.