Two identical non-conducting solid spheres of same mass and charge are suspended in air from a common point by two non-conducting, massless strings of same length. At equilibrium, the angle between the strings is $\alpha$. The spheres are now immersed in a dielectric liquid of density $800 \mathrm{kg} {\mathrm{m}}^{-3}$ and dielectric constant $21$. If the angle between the strings remains the same after the immersion, then

• Correct answer
  A

  electric force between the spheres remains unchanged
• B

  electric force between the spheres reduces
• Correct answer
  C

  mass density of the spheres is $840 \mathrm{kg} {\mathrm{m}}^{-3}$
• D

  the tension in the strings holding the spheres remains unchanged

Hence, the correct answer is options: 'A', 'C'.