For a cubic crystal structure which one of the following relations indicating the cell characteristics is correct ?
a $ \ne $ b $ \ne $ c and $\alpha $ = $\beta $ = $\gamma $ = 90o
a = b = c and $\alpha $ $ \ne $ $\beta $ $ \ne $ $\gamma $ = 90o
a = b = c and $\alpha $ = $\beta $ = $\gamma $ = 90o
a $ \ne $ b $ \ne $ c and ;$\alpha $ $ \ne $ $\beta $ $ \ne $ and $\gamma $ = 90o
