If A→×B→=C→, then
A→ . B→ must be zero
C→ . A→ may be zero
C→ . B→ may be zero
C→.A→+B→ must be zero
Since A→×B→=C→, C→ must be perpendicular to the plane containing A→ and B→. Hence option (4) is correct. Also C→.A→ and C→.B→ must be zero.