516: Solution of washing soda in water is:
(a) Acidic
(b) Basic
(c) Neutral
(d) Sour
517: A merchant wants a gross profit of 25 per cent on the sales. Thus the percentage he should add to the cost price will be:
(a) 25 per cent
(b) 33 per cent
(c) 66 per cent
(d) 75 per cent
518: Which one of the following is the best description of the term 'ecosystem'?
(a) A community of organisms interacting with one another.
(b) That part of the Earth which is inhabited by living organisms.
(c) A community of organisms together with the environment in which they live
(d) The flora and fauna of a geographical area
519: A man starts walking in the north-easterly direction from a particular point. After walking a distance of 500 metres, he turns southward and walks a distance of 400 metres. At the end of this walk he is situated
(a) 300 metres north of the starting point
(b) 100 metres north-east of the starting point
(c) 300 metres east of the starting point
(d) 100 metres north of the starting point
520: After how many days rash appears on the body after the attack of Measles?
(a) One day
(b) Four days
(c) Six days
(d) One week