Classify the following changes as physical or chemical changes. a. Water boils. b. Salt dissolves in water c. Milk turns sour d. A metal rusts.

Water boils - physical change

Salt dissolves in water- chemical change

Milk turns sour- chemical change

metal rusts - chemical change

Explanation:

A chemical change refers to changes that are irreversible and the process involves the evolution of heat along with the formation of a new substance, examples include;Salt dissolves in water, Milk turns sour, metal rusts etc

The boiling of water is a physical change. The water can be cooled and the vapour condensed,hence, the boiling of water is a physical change.

Physical changes are easily reversible and no new substance is formed.

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.  

answers: to make sure that all of the broken pieces of tablet were added to the water, to allow for fair comparison of all three trials, with different particle sizes to avoid experimental error