The radius of a hemispherical balloon increases from 6 cm to 12 cm as air is being pumped into it. The ratio of the surface areas of the balloon in the two cases is

1. 1 : 4

2. 1 : 3

3. 2 : 3

4. 2 : 1

If two solid hemispheres of same base radius r are joined together along with their bases, then the curved surface of this new solid is

1. 4πr²

2. 6πr²

3. 3πr²

4. 8πr²

The volume of the largest right circular cone that can be carved out from a cube of edge 4.2 cm is

1. 9.7 cm³

2. 77.6 cm³

3. 58.2 cm³

4. 19.4 cm³