We do not clean ponds or lakes, but an a | Class 10 Science Chapter Our Environment, Our Environment NCERT Solutions

When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.

Outline a project which aims to find the dominant coat colour in dogs.

Draw the structure for the following compounds.                

       (i)    Ethanoic acid             (ii)   Bromopentane*
       (iii)  Butanone                   (iv)   Hexanal.

*Are structural isomers possible for bromopentane?

A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?

How is the sex of the child determined in human beings?

(a)  What property do all elements in the same column of the Periodic Table as boron have in common?
(b)  What property do all elements in the same column of the Periodic Table as fluorine have in common?

Calculate the number of electrons constituting one coulomb of charge.

A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?

What is an homologous series? Explain with an example.

Why is variation beneficial to the species but not necessarily for the individual?

What are the different methods of contraception?

Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

What is the function of an earth wire? Why is it necessary to earth metallic appliances?

What are the limitations of extracting energy from—

   (a) the wind?          (b) waves?          (c) tides?

Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?

What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.

How is a voltmeter connected in the circuit to measure the potential difference between two points?

How can we explain the reddish appearance of sun at sunrise or sunset? Why does it not appear red at noon?

How are fats digested in our bodies? Where does this process take place?

Give an example of a metal which

  (i) is a liquid at room temperature.
  (ii) can be easily cut with a knife.
  (iii) is the best conductor of heat.
  (iv) is a poor conductor of heat.