Which expression represents a difference of squares?

A. 81 − 49y^2

B. 4x^2 − 16x

C. t^2 + 100

D. 25k − 64

A.    81 - 49y²

Step-by-step explanation:

The triangle that represent a difference of squares is A.

It is easily recognize by looking at the numbers , the number  gives a perfect square and the variable y is also squared

That is 9² = 81                   and         7² = 49  and

Also the sign in-between them must me a negative sign, when the expression consist of the above, then it gives a different of square.

81 - 49y²

9² - 7²y²

(9 - 7y)(9 +7y)

Lets open back the parenthesis to check our answer

(9 - 7y)(9 +7y)

9(9+7y) -7y(9+7y)

81 +63y -63y -49y²

81 - 49y²

the answer is: d) o, f, and kr.

atomic radius of bromine (br) is 114 pm.

atomic radius of oxygen (o) is 73 pm.

atomic radius of fluorine (f) is 72 pm.

atomic radius of krypron (kr) is 112 pm.

the atomic radius of a chemical element is a measure of the size of its atom.

the atomic radius varies with increasing atomic number, but usually increases because of increasing of number of electrons.

the atomic radius decreases across the periods because an increasing number of protons, because greater attraction between the protons and electrons.

step-by-step explanation: