Question

In the scattering experiment the deflection of alpha particle is due to what?

Answer 1

the scattering of alpha particle is due to positively charged nucleus of atom because alpha particles are also positively charged and like charges repel each other that's why they are showing deflection

Answer 2

Yups.
This due to collision of alpha particle with heavy nucleus of atom .
The heavy nucleus of atom rebounds the alpha particle , which causes the scattering since nucleus occupy
${10}^{ - 5}$
area of atom therefore only
${10}^{ - 5}$
alpha particle are rebounds and other just pases over.
hope it helps