In the energy diagram, which number represents the activation energy of the forward reaction?

a (1)
b (2)
c (3)
d (4)

Iknow the answer is a but i don't know why

Sodium nitrite (nano2) reacted with 2−iodooctane to give a mixture of two constitutionally isomeric compounds of molecular formula c8h17no2 in a combined yield of 88%. draw reasonable structures for these two isomers. click the "draw structure" button to launch the drawing utility. place the two compounds in the appropriate boxes below.

37.0 °c = °f (human body normal temperature)