Which of the following is an example of an observation? A. Adding numbers in order calculate the mean.
B. Noting what happens the color of a piece of steel when it is heated.
C. Drying socks in a clothes dryer
D. Placing smelly socks in the washing machine.

B. Noting what happens to the color of a piece of steel when it is heated.

Explanation:

When you observing something you are watching it.

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.  

answerambulatory;