Q31. The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency ' A ' $\times 10 ^ { 12 }$ hertz and that has a radiant intensity in that direction of $\frac { 1 } { { } ^ { \prime } \mathrm { B } ^ { \prime } }$ watt per steradian. ' A ' and ' B ' are respectively\\
(1) 540 and 683\\
(2) 450 and 683\\
(3) 450 and $\frac { 1 } { 683 }$\\
(4) 540 and $\frac { 1 } { 683 }$