Answer: all options presetend by the question apply to indicate that a chemical reaction has taken place
Step-by-step explanation:
The question requires us to choose the signs to identify that a chemical reaction has taken place.
When a chemical reaction happens, some changes in the system can occur indicating that the reactants were converted into products. Some of these changes are:
- formation of gas (or bubbling) when a gas is one of the products of the reaction;
- formation of a solid, also called precipitate, when the product formed is in solid form;
- change in temperature, indicating that the reaction absorbed (decreased temperature) or released (increased temperature) heat;
- change in color, indicating that a product with different color from reactants was formed;
- change in odor.
Therefore, all options presetend by the question apply to indicate that a chemical reaction has taken place.