The QST component is meant to help offset the effect of the Québec sales tax (QST) on the buying power of eligible individuals.
To receive the additional amount for a person living alone, you must have lived alone in a dwelling throughout the previous year. For example, to receive the amount for the period from July 2018 to June 2019, you must have lived alone in a dwelling from January 1 through December 31, 2017.
Note that you are considered to have lived alone if you lived with only one or more people under 18.
For more on the other components of the solidarity tax credit, click Housing Component or Component for Individuals Living in Northern Villages.