How many different spheres of radius $r$ can be drawn which touch all the three coordinate axes?

If the plane $2ax - 3ay + 4az + 6 = 0$ passes through the midpoint of the line joining the centres of the spheres ${x^2} + {y^2} + {z^2} + 6x - 8y - 2z = 13$ and ${x^2} + {y^2} + {z^2} - 10x + 4y - 2z = 8$,then $a$ equals

The centre of the sphere $\alpha \,r^2 - 2u \cdot r = \beta ,(\alpha \ne 0)$ is

The radius of the circle given by the intersection of the sphere $x^2+y^2+z^2+2x-2y-4z-19=0$ and the plane $x+2y+2z+7=0$ is:

The equation ${x^2} + {y^2} + {z^2} = 0$ represents

The radius of the sphere $x^2+y^2+z^2=12x+4y+3z$ is