Question

What is the biggest unit of length?
A. Kilometer
B. Hectometer
C. Decameter
D. Decimeter

Answer 1

We are asked to find the biggest unit of length among the four. We need to compare all the four values of length given in the options. We can see all the four values and comparing these values can result in the right answer.

Complete step by step answer:
Let us start by taking all the four options one by and finally comparing them
(A) The first option on the question is given as, one kilometer. The prefix kilo is used when the unit is multiplied by a thousand.That is,
$1\,km = {10^3}\,m$
We take the values with respect to powers because it is easier to do the comparison and in other cases, it is easier to do the calculation.

(B) The second option on the question is, a hectometre
The prefix Hecto is used when the unit is multiplied by a hundred
That is, $1\,hm = {10^2}\,m$

(C) The third option on the question is decameter. The prefix Deca is used when the unit is multiplied by a ten. That is,
$1\,hm = {10^1}\,m$

(D) The fourth option in the question is decimeter. The prefix Deci is used when the unit is divided by a ten. That is,
$1\,hm = {10^{ - 1}}\,m$
We take ten powers negative one $\left( {{{10}^{ - 1}}} \right)$ instead of one by tenth $\left( {\dfrac{1}{{10}}} \right)$ because, it makes it easier in comparing the powers. If the values are in ten powers, then it makes the comparison very easy. From the four values, we can see that kilometer is the one with the highest power.

Therefore, the right answer is option A.

Note: These terms, before the unit is called, unit prefixes. SI prefixes are used to form decimal multiples and submultiples of SI units. Each prefix has a unique symbol that is prepended to any unit symbol. They are also called metric prefixes. All metric prefixes or unit prefixes used today are decadic. Decadic means that the base is, ten. In this case, ten to the powers.