To break a chemical bond, energy must be(1) absorbed (2) destroyed (3) produced (4) released

1) absorbed

Explanation:

As a chemical bond is formed either by transfer of electrons or sharing of electrons, in order to break the forces of attraction among atoms, energy must be absorbed.

Energy is produced or released when  a chemical bond is formed.

Energy is never destroyed, it converts from one form to another.

percent abundance for cu-63 can be shown as:

63 x + 65 (1-x) = 62.9296

65 - 62.9296 = 2 x

x = 1.035

thus, percent abundance for cu-63 is 1.035

percent abundance for cu-65 can be shown as:

63 x + 65 (1-x) = 64.9278

65 - 64.9278 = 2 x

x = 0.0361

thus, percent abundance for cu-63 is 0.0361

the mass spectrum of cu-63 showing the intense peak as, this isotope is found in nature more abundantly around 92.38 % in comparison to cu-65 which is found 62.58 % naturally