_____gas causes tears in our eyes,while cutting onions.

When dust falls in our eyes, the eyelids close immediately not waiting for our willingness, on touching a hot pan, the hand is withdrawn rapidly. Do you know how this happens?

If we put a cardboard (say 20 cm xx 20 cm) between a light source and our eyes, we can't see the light. But when we put the same cardboard between a sound source and our ear, we hear the sound almost clearly, Explain.

When all colours of visible light strikes the retina of our eye at the same time ,our brain perceives------

List the diseases affecting the eye, their causative agents, impact and Remedial measures.

Which one of the following diseases is caused due to our own body antibodies act against our own boby susbstance?

State the deficiency disease caused by less intake of iron in our diet.