Kilogram
Metric ruler
The gram.
The kilogram.
Grams.
Pounds.
I would use grams.
The unit of weight is the newton, since a weight is a force. However, when people say "weight" they often mean "mass" (or confuse weight with mass); and it is common to talk about a person's mass (or incorrectly, a person's "weight") in kilograms.
An appropriate metric unit of mass for a pencil would be grams.
Weight is a force, so weight is measured in newton. However, when people talk about a person's "weight" they usually mean its "mass" - people tend to confuse that. Mass is measured in kilograms.
You would use kilograms (kg) to measure someone's mass in metric units.
The Newton. However, "weight" and "mass" are often confused; if you want a person's mass, that would be measured in kilograms.
In physics, mass is usually measured in kilograms. Metric weighing-scales will usually display mass in kilograms, so this is a likely choice for the measurement of a person's mass.