During short-circuiting, the current flowing in the electrical circuit increases instantaneously. This occurs because a short-circuit provides a low-resistance path for the current to bypass its normal route through the circuit components. As a result, a large amount of current flows through the short-circuit path, causing an instantaneous increase in the overall current in the circuit.

Option 1, which states that the current reduces substantially during short-circuiting, is incorrect. Short-circuiting actually results in an increase in current, not a decrease.

Option 2, which claims that the current does not change during short-circuiting, is also incorrect. The current definitely changes and increases during short-circuiting.

Option 4, which suggests that the current varies continuously during short-circuiting, is not accurate either. Short-circuiting causes a sudden, drastic increase in current rather than a continuous variation.

In summary, during short-circuiting, the current flowing in the electrical circuit increases instantaneously.