Subtract 2.5×10^-5 from 8.0×10^-3 with regards to significant numbers.

8.0 x 10⁻³

Explanation:

(8.0×10⁻³)  - (2.5×10⁻⁵)

= (8.0×10⁻³)  - (2.5 × 10⁻² x 10⁻³)   (factor out 10⁻³)

= 10⁻³  [ 8 - (2.5 x 10⁻²) ]

= 10⁻³  [ 8 - 0.025 ]

= 10⁻³  [ 7.975 ]

= 7.975 x 10⁻³

however we can observe that both original numbers are expressed to 2 significant figures, hence we must express our answer also in 2 significant figures by rounding 7.975 to 8.0, thereby giving us:

8.0 x 10⁻³

beta is electron from nucleus

something from nucleus has changed, but charge must be same for cons of charge