How does the acceleration due to gravity change with altitude?

If the value of acceleration due to gravity on the surface of the Earth is $g$,what will be the value of $g$ at a height equal to the radius of the Earth from the surface?

The force of gravity is least at:

$T$ is the time period of a simple pendulum on the Earth's surface. Its time period becomes $xT$ when taken to a height $R$ (equal to the Earth's radius) above the Earth's surface. Then,the value of $x$ will be:

The value of $g$ at a particular point is $9.8\,m/s^2$. Suppose the Earth suddenly shrinks uniformly to half its present size without losing any mass. The value of $g$ at the same point (assuming that the distance of the point from the centre of the Earth does not shrink) will now be ......... $m/s^2$.

Which of the following statements are true about the acceleration due to gravity,$g$?
$A$. $g$ is greater at the poles.
$B$. The value of $g$ decreases with height.
$C$. The value of $g$ is the same all over the Earth.
$D$. The value of $g$ is maximum at the center of the Earth.