optical and radio telecopes are build on ground but X-ray astronomy is possible only from satellites or biting the earth. Explain why?

our earth has several artificial satellites but the moon is the only natural satellite. distance to the moon from the Earth is 3.84×10^8m and the time period of moon's revolution is 27.3 days. obtain the mass of earth. (gravitational constant G=6.67×10^(-11)Nm^2kg^(-2)

Apart from tetrahedral geometry, another possible geometry for 'CH_4' is square planar with the four H atoms at the corners of the square and the Catom at the centre. Explain why 'CH_4' is not square planar.

Choose the electronic configurations that are possible from among the following. Explain why the others are impossible. a '1 s^2 2 s^3 2 p^6' b '1s^2 2 s^2 2 p^4' C '1 s^2 2 s^2 2 p^8 3 s^2 3 p^6 3 d^7' d '1 s^2 2 s^2 2 p^6 3 s^2 3 d^9'

In a sample of hydrogen atoms, electrons jump from 10^(th) excited state to ground state. If X are the number of different ultraviolet radiations Y are the number of different visible radiations and Z are the possible number of different infrared radiations from 10^(th) excited state to third level. The value Z-(x + y) is (Assuming all the Balmer lines lie with in visible region)

Our earth has several artificial satellites but the moon is the only natural satellite. How do you explain weightlessness in an artificial satellite?