Explain the change that can be observed in the characterstics of river water when sewage is discharged into it and a few weeks after the discharge with respect to
(i) level of dissolved oxygen
(ii) Population of fresh water organisms.

Study the graph given below. Explain how is oxygen concentration affected in the river when sewage is discharged into it.

Explain the process of sewage water treacment before it can be discharged into natural water bodies . Why is this treatment essential ?

Explain the process of sewage water treatment before it can be discharged into natural water bodies . Why is this treatment essential ?

A student puts his pencil into an empty trough and observes the pencil from the position as indicated in Figure. (i) What change will be observed in the appearance of the pencil when water is poured into the trough? (ii) Name the phenomenon which accounts for the above stated observation. (iii) Complete the diagram showing how the student's eye sees the pencil through water.

When domestic sewage mixes with river water (a) small animals like rats will die after drinking river water (b) the increased microbial activity releases micronutrients such as iron (c) the increased microbial activity uses up dissolved oxygen (d) the river water is still suitable for drinking as impurities are only about 0.1 %

Explain the following with proper reason: (i) Bleaching of flowers by chlorine is permanent while after bleaching with SO_2 , the colour returns. (ii) Iodine dissolves more in KI solution than in water.

(a) A student dropped a few pieces of marble in dilute hydrochloric acid contained in a test tube. The evolved gas was passed through lime water. What change would be observed in lime water ? Write balanced chemical equations for both the changes observed. (b) State the chemical property in each case on which the following uses of baking soda are based: (i) as an antacid (ii) as a constituent of baking powder.

When a boat travels in a river (strictly in a straight line), it can go either in the direction of flow of river (i.e downstream) or in the direction opposite the flow of river (i.e. upstrem ). Thus the boat's actual speed is more than by which it can move in stationary water while travelling downstram (as river's flow speed is added to it) and less while travelling upstream (as the boat moves against the flow of river).Based on the given information answer the following questions A boat going downstream in a following river overcome a raft at a point P. 1 h later it turned back and after some time passed the raft at a distance 6 km from point P. Find the speed of river

When a boat travels in a river (strictly in a straight line), it can go either in the direction of flow of river (i.e downstream) or in the direction opposite the flow of river (i.e. upstrem ). Thus the boat's actual speed is more than by which it can move in stationary water while travelling downstram (as river's flow speed is added to it) and less while travelling upstream (as the boat moves against the flow of river).Based on the given information answer the following questions A boat going downstream in a following river overcome a raft at a point P. 1 h later it turned back and after some time passed the raft at a distance 6 km from point P. After reversing its direction ,how much time was taken by the boat to meet the raft again ( i.e. 2^(nd) time) ?

A car has a fresh storage battery of emt 12 V and internal resistance 5.0 xx 10^(-2) Omega . If the starter moter draws a current of 90A, what is the terminal voltage of the battery when the starter is on? (b) After long use, the internal resistance of the storange battery increase to 500 Omega . What maximum current can be drawn from the battery? Assume the emt of the battery to remain unchanged. (c) If the discharged battery is changed by an external emf source, is the terminal voltage of the battery during changing greater of less than is emf 12 V ?