Plz solve 2 10 9 8 7

Dear Student,
(2.) According to Gauss's law 
Φ_E = Q_enclosed/ϵ₀
If the radius of the Gaussian surface is doubled, the outward electric flux will be remain the same. This is because electric flux depends only on the charge enclosed by the surface. 
Hence, option d is correct.

(7.) The relative permeability is given by,
Relative permeability = Permeability of a substance/ Permeability of vaccum 
81 = ε_{​​​​​​w}/ε₀
81ε₀ = ε_w 
ε_{​​​​​​w} = 81 ε₀ (option D)

Kindly post the different questions in different thread.

Regards