Two types of balances, the beam balance and the spring balance are commonly used for measuring weight in shops. If we are on the moon, we can continue to use

The correct answer is: Only the beam type balance without any change

Let us understand the working principles of both types of balances to see how they behave under different gravitational conditions, such as on the Moon.

1. Beam Balance:
A beam balance compares an unknown mass ($m_1$) against a known standard mass ($m_2$). It works on the principle of moments. Under a gravitational acceleration $g$, the gravitational forces (weights) acting on the two pans are:
$W_1=m_{1}g$
$W_2=m_{2}g$
When the beam is balanced, the torques or forces on both sides are equal:
$m_{1}g=m_{2}g$
Since the local acceleration due to gravity ($g$) appears on both sides of the equation, it cancels out:
$m_1=m_2$
Because the measurement depends strictly on the comparison of the two masses and is independent of the value of gravity, a beam balance calibrated on Earth will still give correct readings on the Moon (where gravity is approximately 1/6th of Earth's gravity) without requiring any changes or recalibration.

2. Spring Balance:
A spring balance measures weight based on Hooke's Law, where the extension of the spring ($x$) is directly proportional to the downward gravitational force (weight $W$) acting on the suspended mass ($m$):
$F=kx=mg$
Here, $k$ is the spring constant. The extension $x$ is given by:
$x=\frac{mg}{k}$
Since the spring balance measures the extension directly, its reading depends heavily on the local acceleration due to gravity ($g$). On the Moon, where gravity is much weaker, the same mass will stretch the spring much less (about 1/6th of the extension on Earth). Thus, a spring balance calibrated on Earth will show an incorrect, much lower reading on the Moon unless it is recalibrated.

Therefore, we can continue to use only the beam type balance without any change.