Assertion (A): Nichrome is an alloy which is commonly used in electrical heating devices such as electric irons, toasters, etc.

Reason (R): The resistivity of nichrome is high and its resistance decreases with increase in temperature.

The chapter states directly: 'Table 11.2 reveals that the resistivity of an alloy is generally higher than that of its constituent metals. Alloys do not oxidise (burn) readily at high temperatures. For this reason, they are commonly used in electrical heating devices, like electric iron, toasters etc.' Nichrome (an alloy of nickel, chromium, manganese and iron, per Activity 11.1) has resistivity $100\times10^{-6}~\Omega\,\mathrm{m}$ (Table 11.2), much higher than its constituent metals, making Assertion A true.

However, Reason R is false: the chapter never states nichrome's resistance decreases with rising temperature; rather it notes 'Both the resistance and resistivity of a material vary with temperature,' and for metals and alloys resistance generally increases with temperature. Nichrome is chosen for heating devices because of its high resistivity and resistance to oxidising at high temperatures, not because its resistance decreases with heat.

(A) Both true, R correct explanation: incorrect because R's claim of decreasing resistance with temperature is false.

(B) Both true, R not correct explanation: incorrect because R itself is false, not merely an unrelated true statement.

(D) A false, R true: incorrect because A is true (nichrome's high resistivity and heat-resistance are exactly why it is used in heating devices), while R is false.