Physical Quantities and Measurement

3500 m

Step 1: Recall the relation: 1 km = 1000 m. Step 2: To convert km to m, multiply by 1000. Step 3: 3.5 km = 3.5 × 1000 m = 3500 m. Step 4: Option 350 m is wrong – this would be dividing instead of multiplying. Option 35000 m means multiplying by 10000, which is incorrect. Option 0.0035 m is dividing by 1000, which converts m to km, not the other way. The correct answer is 3500 m.

Kilogram (kg)

Step 1: Mass is the quantity of matter contained in a body. Step 2: The S.I. system assigns standard base units to basic physical quantities. Step 3: The S.I. unit of mass is kilogram, written in short as 'kg'. Step 4: Gram (g) is a sub-multiple of kilogram (1 g = 10⁻³ kg). Milligram is an even smaller unit. Quintal is a multiple (1 quintal = 100 kg). None of these are the S.I. base unit. The correct answer is kilogram.

2500 g

Step 1: Recall the relation between kilogram and gram: 1 kg = 1000 g. Step 2: To convert kg to g, multiply by 1000. Step 3: 2.5 kg = 2.5 × 1000 g = 2500 g. Step 4: Option 250 g uses a multiplier of 100, not 1000, so it is wrong. Option 25 g is far too small. Option 25000 g uses a multiplier of 10000, which is incorrect. The correct answer is 2500 g.

Electronic balance

Step 1: A beam balance works by comparing the unknown mass with standard weights placed on the pans. It is good for general measurements but not very precise for tiny masses. Step 2: An electronic balance converts the load into an electrical signal and displays the mass digitally. It can measure masses as small as 1 mg. Step 3: Electronic balances are precise and automatic – no separate weight box is needed. Step 4: Spring balance measures force (weight), not mass directly. A measuring tape measures length. The electronic balance is the correct choice for precise, small mass measurements.