State one basic difference between a physical change and a chemical change.

Name the ores of mercury.

Name a non-metal which is lustrous and a metal which is non-lustrous. 

Which pancreatic enzyme is effective in digesting proteins?

A wire of resistance 10 ohm is bent in the form of a closed circle. What is the effective resistance between the two points at the ends of any diameter of the circle?

Name the carbon compound which on heating with excess of concentrated sulphuric acid at 443 K gives ethene.

Name a functional group present in 
(i) CH₃CHO
(ii) C₂H₅COOH

Feather imprints were preserved along the dinosaur's bones but dinosaurs could not fly. What was the significance of feathers in reptiles and later on for other species?

Find the power of a concave lens of focal length 2m.

Give an example of a phenomenon where Tyndall effect can be observed.

A shiny brown coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and the black coloured compound formed.

In the reaction:
2KClO₃ \(\overset { \Delta/MnO_2 }{ \rightarrow } \) 2KCl + 3O₂, what does the '\(\Delta\)' and 'MnO₂' signify? What type of reaction is this?

What happens when nitric acid is added to egg shell?

Explain the role of mouth in digestion of food.

What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?

(i) An aqueous solution has a pH value of 7.0.  Is this solution acidic, basic or neutral?

(ii) If H+ concentration of a solution is \(1\times 10^{-2}\ mol\ L^{-1},\) what is the pH value for it?

(iii) Which has a higher pH value, 1 M HCl or 1 M NaOH solution?

(i)Two solutions X and Y are tested with universal indicator. Solution X turns orange whereas solution Y turns red. Which of the solutions is a stronger acid?
(ii) State the meaning of strong acids and weak acids. Give one example of each.

(i) What is meant by the term hydrated salt?
(ii) Give two examples of hydrated salt which are white and state their chemical formula.

Write one example of each of the following:
(i) Most malleable metal and most ductile metal.
(ii) The best conductor of heat and the poorest conductor of heat.
(iii) A metal with highest melting point and a metal with lowest melting point.

A touch bulb is rated 2.5 V and 750 mA. Calculate (i) its power, (ii) its resistance and (iii) the energy consumed if this bulb is lighted for four hours.

(a) What is corrosion of metals? Name one metal which does not corrode and one which corrodes on being kept in atmosphere.
(b) How will you show that the rusting of iron needs oxygen and moisture at the same time?

Name various plant hormones. Also give their physiological effects on plant growth and development.

(i) One half of a convex lens of focal length 10 cm is converted with a black paper. Can such a lens produce an image of a complete object placed at a distance of 30 cm from the lens? Draw ray diagram to justify your answer.
(ii) A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 15 cm. Find nature, position and size of the image.

(a) Draw a ray diagram to show the formation of image by concave lens when an object is placed in front of it.
(b) In the above diagram mark the object -distance (u) and the image-distance (v) with their proper signs (=ve or -ve as per the new Cartesian sign convention) and state how these distance are related to the focal length (f) of the concave lens in this case.
(c) Find the nature and power of a lens which forms a real and inverted image of magnification -1 at a distance of 40 cm from its optical centre.

Suggest any four activities in daily life which are eco-friendly.