What quantity is represented by the metric system prefix deci-?

Answer :  The quantity represented by the metric system prefix deci- is 0.1

Explanation :

Metric system : The Metric System measured the things in meters, grams, liters, etc and adds prefixes like kilo, milli and centi to the count orders of the magnitude.

In metric system, a metric prefix is a unit prefix that comes before the basic unit of measure to indicate the fraction of the unit.

Metric system                 (factor)                      Prefix Symbol

1000                                   kilo-                                 k

100                                     hecto-                              h

10                                       deca-                               da

0.1                                       deci-                                d

0.001                                  centi-                                c

0.0001                                milli-                                 m

0.0000001                        micro-                               μ

Hence, according to the metric system the quantity represented by the metric system prefix deci- is 0.1

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.