A photograph measuring 10cm by 4cm is mounted on a rectangular cardboard leaving a margin of 3cm all around. A. what is the area of the photograph?

b. what is the area of the cardboard?

c. what is the area of the cardboard is not covered by the photograph?​

not clear

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.

the answer is na (sodium)

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.