Q1 Assertion : When we change the unit of measurement of a quantity, its numerical valuechanges.Reason : Smaller the unit of measurement smaller is its numerical value.Q2 Assertion: Parallax method cannot be used for measuring distances of stars more than 100light years away.Reason: Because parallax angle reduces so much that it cannot be measured accurately.Q3 Assertion: Number ofsignificant figures in 0.005 is one and that in 0.500 is three.Reason: This is because zeros are not significant.Q4 Assertion: Out of three measurements l= 0.7m , l=0.70 m and l=0.700m is most accurate.Reason: In every measurement, only the last significant digit is not accurately known.Q5 Assertion: Nowadays a standard meter is defined in terms of wavelength of light.Reason: light has no relation with length.

Q1: Assertion: True. The numerical value of a quantity does change when we change the unit of measurement. For example, 1 kilometer is equal to 1000 meters. So, the numerical value changes from 1 (in km) to 1000 (in m). Reason: True. The smaller the unit of measurement, the larger the numerical value. For example, 1 kilometer is equal to 1000 meters. So, the numerical value changes from 1 (in km) to 1000 (in m).

Q2: Assertion: True. The parallax method becomes less accurate for measuring distances of stars more than 100 light years away because the parallax angle becomes too small to measure accurately. Reason: True. The parallax angle reduces so much that it cannot be measured accurately for stars more than 100 light years away.

Q3: Assertion: True. The number of significant figures in 0.005 is one (5) and that in 0.500 is three (5, 0, 0). Reason: False. Zeros are significant if they are between other significant figures or if they are at the end of a decimal number.

Q4: Assertion: True. The measurement l=0.700m is the most accurate because it has the most significant figures. Reason: True. In every measurement, only the last significant digit is not accurately known, so the more significant figures, the more accurate the measurement.

Q5: Assertion: True. Nowadays a standard meter is defined in terms of the wavelength of light from a specified transition in krypton-86. Reason: False. Light does have a relation with length. The speed of light is a constant and can be used to define length.