An iron pipe 20 cm long has exterior diameter equal to 25 cm. If the thickness of the pipe is 1 cm, then the whole surface of the pipe is

Given,

The length of iron pipe (h) = 20 cm

External diameter = 25 cm, then external radius will be (R) = 12.5 cm

Internal diameter = 25 - (2) = 23 cm (as thickness of the pipe is 1cm), then internal radius will be (r) = 11.5cm

Total surface area of the pipe = External curved surface area + Internal curved surface area + 2 (Base area)

$$\Rightarrow$$ 2$$\pi$$Rh + 2$$\pi$$rh + 2$$\pi$$(R$$^{2}$$ - r$$^{2}$$)

$$\Rightarrow$$ 2$$\pi$$h(R + r) + 2$$\pi$$(R$$^{2}$$ - r$$^{2}$$)

$$\Rightarrow$$ 2($$\frac{22}{7}$$)(20)(24) + 2($$\frac{22}{7}$$)(24)

$$\Rightarrow \frac{44 \times 24 \times 21}{7}$$ = 3168 cm$$^{2}$$

Hence, option C is the correct answer.