A remote-sensing satellite of earth revolves in a circular orbit at a height of $0.25\times {10}^6$ m above the surface of earth. If earth's radius is $6.38\times {10}^6\mathrm{ }\mathrm{m}$ and $\mathrm{g}=9.8\mathrm{ }\mathrm{m }{\mathrm{s}}^{-2}$, then the orbital speed of the satellite is:
Mass of earth undefined

• A

  $8.56\mathrm{ }\mathrm{k}\mathrm{m}\mathrm{ }{\mathrm{s}}^{-1}$
• B

  $9.13\mathrm{ }\mathrm{k}\mathrm{m}\mathrm{ }{\mathrm{s}}^{-1}$
• C

  $6.67\mathrm{ }\mathrm{k}\mathrm{m}\mathrm{ }{\mathrm{s}}^{-1}$
• Correct answer
  D

  $7.76\mathrm{ }\mathrm{k}\mathrm{m}\mathrm{ }{\mathrm{s}}^{-1}$

Hence, the correct answer is option: 'D'.