At a certain place, the acceleration due to gravity is determined usin...
To find the accuracy (i.e. error) in measurement of g, first let's see what all we need to find.
We know, $T=2\pi\sqrt{\frac{l}{g}}$
i.e., $g = 2\pi \frac{l}{T^2}$
i.e., $\delta g = \delta l + 2 \cdot \delta T$
where $\delta a$ denotes percentage error in $a$.
To find percentage error in length, we can see that the reading is given 25.0 cm, i.e. applying knowledge of significant figures, the least count of the instrument should be 0.1cm.
Thus, $\delta l = \frac{0.1}{25.0} \times 100$
or, $\delta l = 0.4%$
Also, least count of the stopwatch is given to be 1s. And the reading is 50 s.
So, $\delta T = \frac{1}{50} \times 100$
i.e., $\delta T= 2%$
Now, we had already found that $\delta g = \delta l + 2 \cdot \delta T$
Putting in values for $\delta l$ and $\delta T$, we find that $\delta g = 4.40%$