The height in terms of radius of the earth \((R)\), at which the acceleration due to gravity becomes \(\dfrac{g}{9},\) where \(g\) is acceleration due to gravity on earth's surface, is:
1. \(\sqrt{3}{R}\)
2. \({2}\sqrt{2}{R}\)
3. \(2R\)
4. \(\dfrac{4}{9}R\)