Some students observe four different lab investigations. The students record their observations in a table. Investigation
Observations
1
A beaker of water is
heated on a hot plate. Bubbles form in
the water, and steam is given off.
2
Oil is added to a beaker of water. Oil forms a layer on top
of the water
3
Sand and iron filings are mixed in a beaker. A magnet is
then used to separate the iron filings from the sand.
4
A piece of chalk is placed in a beaker of vinegar Bubbles
form as a gas is given off.
Which investigation most likely involved a chemical reaction?

Number 4 is an example of a chemical reaction

Explanation:

heThe chalk is reacting with the vingear which is creating a new substance. The new substance is the gas that the reaction gives off.

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.