(a) How does the painting of an iron object prevent its rusting?
(b) How does the electrical conductivity of copper alloys, brass ad bronze, differ from that of pure copperr?
(c) What is meant by 22 carat gold? Name the metals which are usually alloyed with gold to make it harder.

(a). What is an alloy? How is an alloy made? (b) What elements are preent in steel? How are the properties of steel different from those of pure iron? (c) give the constituents ad one use of brass.

(a) If a patient is advised anti-retroviral drug, name the possible infection he/she is likely to be suffering from. Name the causative organism. (b) How do vaccines prevent subsequent microbial infection by the same pathogen? (c) How does a cancerous cell differ from a normal cell? (d) Many microbial pathogens enter the gut of humans along with food. Name the physiological barrier that protects the body from such pathogens.

Explain the following : (a) Why is tungsten used almost axclusively for filament of incandescent lamp ? (b) Why are the conductors of electric heating devices, such as toaster and electric irons, made of an alloy rather than a pure metal ? ( c) Why is the series arrangement not used for domestic circuits ? (d) How does the resistance of a wire vary with its cross-sectional area ? (e ) Why are copper and aluminimum wires usually employed for electricity transmission.

(a) What do you understand by the term 'variation' ? (b) Name two human traits which show variation . (c) How does the creation of variation in a species ensure its survival ?

Fill in the following blanks with suitable words: ltbr. (a). The corrosion of iron is called. (b) _____ and ____ are necessary for the rusting of iron. (c). The process of depositing a thin layer of zinc on iron articles in called. (d). Tiffin boxes are electroplated with ____but car bumbers are electroplated with ______to protect them fro rusting (e) The corrosion of copper produces a_____coating of basic copper carbonate on its surface. (f). Brass in an alloy of copper and ____ (g) Bronze is an alloy of copper and_____ (h) The non-metal present in steel is_____ (i) The alloy in which one of themtals is mecury is called an _____ (j) the electrical conductivity and melting point of an alloy is_____than that of pure metals. (i) The rocky material found with ores is called._____

(a). What is meant by the reactivity series of metals? Arrange the following metals in an increasing order of their reactivities towards water: Zinc, Iron, Magnesium, Sodium. (b). Hydrogen is not a metal but still it has been assigned a place in the reactivity series of metals. Why? (c). Name one metal more reactive ad another less reactive than hydrogen. (d). Name one metal which displaces copper from copper sulphate solution and one which does not. (e). name one metal which displaces silver from silver nitrate solution and one which does not.