The correct option is B √3
Given that →a,→b,→c are mutually perpendicular, so,
→a.→b=→b.→c=→c.→a=0
and →a,→b and →c are unit vectors, so
|→a|=|→b|=|→c|=1
Now, →c are unit vectors, so
|→a+→b+→c|2=|→a|2+|→b|2+|→c|2+2→a.→b+2→b.→c+2→c.→a
⇒|→a+→b+→c|2=3
∴|→a+→b+→c|=√3