Could anybody help with part a and b ??

The answer to part A is the last option ( at the bottom) because we know that he bought one notebook, but we don't know how many pens he bought. The answer to part b would be 12 pens. To get the part b answer you simply solve for the variable p in the equation. Hope this helps! Have a nice day!

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.