Our senses are not reliable for accurate measurement.

Option $(B)$ is correct because a clock can measure time correctly up to one second. A stopwatch can measure time correctly up to a fraction of a second. A digital watch can measure time up to a fraction of second whereas an atomic clock is the most accurate timekeeper and is based on characteristic frequencies of radiation emitted by certain atoms having a precision of about $1$ second in $300,000$ years. So an atomic clock can measure time most precisely as the precision of this clock is about $1 s$ in $10^{13} s$.

For a screw gauge, the precision in measurement is depends on the least count. The smaller least count will give the more precision. Since student C has measured diameter using screw gauge with smallest least count so the measurement will more precise for student C.   

The accuracy is how close the measured value with the true value. The true value is the average value of the measurements. Thus when more number measurements will be taken, the accuracy will be more. Since student B has taken more readings, so the measured value for B will be most accurate.   

Since the measured value of weight of the substance is far away from the value of actual weight, so the measurement is said to be inaccurate.

Accuracy is defined as the extent upto which a given measurement agrees with the standard value for that measurement whereas the degree to which several measurement provide answer very close to each other is known as precision.
Since the measurements are close to the known value. so these measurements are accurate but these are far from each other, these are not precised.

Accuracy defines nearness of a measured value to the standard or true value. Since value measured by student 1 is nearer to the actual value $12 \ kg$ compared to that measured by student 2. So measurement of student 1 is more accurate.

Accuracy is defined as the extent upto which a given measurement agrees with the standard value for that measurement.
For example : Actual weight of the given substance is $10.0 \ kg$ and the measured value of the mass is $9.9 \ kg$. This measurement is said to be accurate.

Accuracy is defined as the extent upto which a given measurement agrees with the standard value for that measurement. Accuracy refers to the degree of conformity and correctness of something when compared to a true or absolute value.

Precision refers to a state of strict exactness.
For example : Let the true weight of given substance is 12 kg.
The values of three measurements obtained by student are 10.1, 10.2 and 10.3. Then the measurements are said to be precise.

Accuracy is defined as the extent upto which a given measurement agrees with the standard value for that measurement whereas the degree to which several measurement provide answer very close to each other is known as precision.
Since the measured values are very close to each other, then the measurements are said to be precised.

The degree to which several measurement provide answer very close to each other is known as precision.For example : Let the true weight of given substance is 12 kg.
The values of three measurements obtained by student are 10.1, 10.2 and 10.3. Then the measurements are said to be precise.

Accuracy of potentiometer can be easily increased by decreasing the potential gradient across the potentiometer wire and that can be done by increasing its length.

The degree to which several measurement provide answer very close to each other is known as precision. In other words, precision reflects the quality of measuring instrument.

Force$(f)=\cfrac{mv^2}{r}=\cfrac{4\times(10)^2}{8}=50\ \therefore\cfrac{\Delta F}{F}=\cfrac{\Delta m}{m}+2(\cfrac{\Delta V}{V})+(\cfrac{\Delta r}{r})\ \quad=\cfrac{0.1}{4}+2\cfrac{(0.1)}{10}+\cfrac{0.8}{8}\ \therefore \cfrac{\Delta F}{F}=0.07$

According to the problem, the length L = 5 cm 

 Metals like iron can be used to shield the instruments from external magnetic fields because magnetic fields cannot penetrate metallic surfaces.

Given,

The one with more significant figures in the decimal is more accurate.
Option D.

In addition or subtraction we can reduce the terms to least accurate term and add or subtract them. By this process in addition or subtraction answer is not much get affected or change in answer is negligible.