Critical frequency \[{{v}_{c}}\] for the ionosphere is - – McqOptions

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1.	Critical frequency \[{{v}_{c}}\] for the ionosphere is -
A.	\[{{v}_{c}}=9.{{N}_{\max }}\]
B.	\[{{v}_{c}}=9\sqrt{{{N}_{\max }}}\]
C.	\[{{v}_{c}}=6.IN\max \]
D.	\[{{v}_{c}}=6.{{N}_{max}}\]
Answer» C. \[{{v}_{c}}=6.IN\max \]

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