Gram.
The metric (SI) unit for weight is the newton, since weight is a force. When people talk about "weight", they sometimes actually mean "mass". The unit for mass is the kilogram.
a ruler
Gram.
Tonnes
grams
Meters
The metric standard unit of mass is the kilogram (Kg).
The basic metric unit of mass is the gram (g).
The gram is a unit of mass in the metric system.
Milligrams.
The SI unit for mass in the metric system is the kilogram.
The basic unit of mass in the metric system is the gram.
A neutron is an electrically neutral subatomic particle. A Newton is the metric unit of force. A Kilogram is the metric unit of mass. We have no idea what a 'newtron' is.
The metric unit for measuring mass is the kilogram (kg). Other common units include the gram (g) and the metric tonne (t).
The standard unit in the metric system for measuring mass is the kilogram (kg).
An appropriate metric unit of mass for a pencil would be grams.