That depends what aspect of the aeroplane you're measuring.
An aeroplane's length would be measured in metres, as would its height.
The mass of the aeroplane would be in kilograms.
Its speed would be in metres per second or more traditionally kilometres per hour.
A metre.
Liters or gallons are appropriate metric units for measuring the capacity of a picnic cooler.
A dekameter would be the appropriate, but rarely used, unit.
di ko alam....
A litre.
The appropriate metric unit to measure the mass of a lawn mower would be kilograms (kg). This unit is commonly used for measuring the weight of objects in metric system.
None, really, because a gallon is not a metric unit. A litre is the appropriate unit to use for measuring volumes.
measuring temperature the metric system of °C is used.
An appropriate metric unit of mass for a pencil would be grams.
The SI (metric) unit for mass is the kilogram.
gram
meter