Sheela's teacher said in her classroom that we should not dispose of motor oils and medicines in the drain. Why did her teacher say this statement?

Why 

 the image in concave mirror is always form real and inverted image 

Concave mirror always form real and inverted image

Difference between concave and convex lens, concave and convex mirror

What is light? What are different types of light ?

I wanted a PDF of the notes but there is no pdf. the topic is reproduction in plants chapter 12 so can you please send a pdf or unable the words to do a copyright or  i have  to write it all please reply  its urgent.....