# Question #12530

##### 1 Answer

The answer is **c)**

#### Explanation:

The idea here is that you must use the density of water to convert the given volume to *grams*

#18 color(red)(cancel(color(black)("mL"))) * "1 g"/(1color(red)(cancel(color(black)("mL")))) = "18 g"#

Now, the **molar mass** of water is approximately equal to **mole** of water has a mass of

You can thus say that your sample of water is equivalent to **mole** of water. As you know, **mole** of water must contain **molecules** of water **Avogadro's constant**.

You can thus say that your sample contains **molecules** of water.

To find the number of electrons present in the sample, calculate the number of electrons present in **molecule** of water. To do that, grab a Periodic Table and look for the *8atomic numbers** of the two elements that make up the water molecule

#"For H: " Z = 1#

#"For O: " Z = 8#

As you know, a neutral atom has **equal numbers** of protons inside its nucleus and electrons surrounding its nucleus. This implies that **molecule** of water will have a total of

#"no of e"^(-)color(white)(.)"in 1 molecule" = overbrace(2 xx "1 e"^(-))^(color(blue)("from 2 atoms of H")) + overbrace(1 xx "8 e"^(-))^(color(purple)("from 1 atom of O")) = "10 e"^(-)#

Therefore, the total number of electrons present in your sample will be equal to

#6.02 * 10^(23) color(red)(cancel(color(black)("molecules H"_2"O"))) * "10 e"^(-)/(1color(red)(cancel(color(black)("molecule H"_2"O")))) = 6.02 * 10^(24)# #"e"^(-)#