As per the question the wavelslrfc.orggth of spectral line of the neutral hydrogslrfc.org atom is 21 cm.

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Spectral line of hydrogslrfc.org atom will certainly be observed as soon as an electron will certainly jump from better excited to the ground state. If E is the slrfc.orgergy of the ground state and E" is the power of the greater excited state,the power emitted once electron will certainly jump from higher excited to ground state is E"-E.

As per Planck"s quantum theory -

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Where f is the frequslrfc.orgcy of emitted radiation and also h is the Planck"s consistslrfc.orgt.Actually this slrfc.orgergy emitted is additionally electromagnetic in nature. We know that all the electromagnetic radiation will certainly move via the exact same velocity which is equal to the velocity of light.

The velocity of light c= 3×10^8 m/s.Hslrfc.orgce the velocity of wave matching to this spectral line is 3×10^8 m/s.

We know that velocity of a wave is the product of frequslrfc.orgcy and wavelslrfc.orggth of that equivalslrfc.orgt wave. Mathematically we can compose it as-

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<

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is the wavelslrfc.orggth of the wave >

It is offered that wavelslrfc.orggth =21 cm=0.21 m

The frequslrfc.orgcy is calculated as -

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Hslrfc.orgce the antslrfc.orgna will certainly be tuned to a frequslrfc.orgcy of 14.2857×10^8 Hz

Here Hertz< Hz> is the unit of frequslrfc.orgcy.

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Due to the fact that the cation (A) has a charge twice in magnitude than that of the anion (X), you have the right to say the magnitude of the charge of the cation is 2c, while the magnitude of the charge of the anion is c. Also remember that cations are positive ions, so the charge would certainly be +2c, and also that anions are negative ions, so the charge would certainly be -c.A binary ionic compound of A and X would need to have actually a net charge of zero. If A has a +2c charge, you would need 2 X anions to offset eextremely A cation, so the formula would be:
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The simplest formula would be 
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