1000 solid spherical balls each of radius 0.6 cm are melted and recast into a single spherical ball. What is the surface area (in cm$$^2$$) of ball so formed?

When casting is done from one shape to another, Volume will remain same.

Volume of sphere = $$\frac{4}{3}\pi\ r^3$$

According to question, 

$$n\times\ \frac{4}{3}\times\ \pi\ \times\ r^3=\frac{4}{3}\times\ \pi\ \times\ R^3$$

n = number of balls 

r = radius of small balls

R = radius of single big ball

$$\therefore\ 1000\times\ \frac{4}{3}\times\ \pi\ \times\ \left(0.6\right)^3=\frac{4}{3}\times\ \pi\ \times\ R^3$$

$$\therefore\ 216=\ R^3$$

$$\therefore\ R\ =\ 6\ cm$$

Surface area of sphere = $$4\pi\ r^2$$

= $$4\pi\ \times\ 6^2\ =\ 144\pi\ $$

Hence, Option A is correct.