How many significant digits are there in the number 204.0920?

7 significant digits

Explanation:

Significant  digits.: The figures in a number which express the value -the magnitude of a quantity to a specific degree of accuracy is known as significant digits.

Rules for significant figures:

Digits from 1 to 9 are always significant and have infinite number of significant  digits.

All non-zero numbers are always significant. For example: 654, 6.54 and 65.4 all have three significant  digits.

All zero’s between integers are always significant. For example: 5005, 5.005 and 50.05 all have four significant digits.

All zero’s preceding the first integers are never significant. For example: 0.0078 has two significant digits.

All zero’s after the decimal point are always significant. For example: 4.500, 45.00 and 450.0 all have four significant digits

Thus 204.0920 has 7 significant digits.

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.  

the answer your looking for is c).