Two identical coils are placed coaxially. They carry equal currents in the same direction. Then

Question

$\begin {array} {1 1} (a)\;On\: their\: axis \: there \: are\: three\: points\: where\: the\: net\: field\: is\: zero \\ (b)\;On\: their\: axis \: there \: are\: two\: points\: where\: the\: net\: field\: is\: zero \\ (c)\;On\: their\: axis \: there \: is\: no\: points\: where\: the\: net\: field\: is\: zero \\ (d)\;On \: moving\: from\: centre\: of\: one\: coil \: to \: the \: centre\: of\: another, \: the \: field\; first\: increases\: and\: then\: decreases \end {array}$