Cells which are not dividing are likely to be at

1.  G1

2.  G2

3.  G0

4.  S-phase

Class 11 pg 164
(c) G0 ,G signifies growth. and zero means no growth takes place at this stage. It is also called quiescent stage (G0). Some cells of the body like heart cells, neuron which do not divide, exit at G1 stage and enter G0 of the cell cycle which is an inactive stage.
The cells in this stage remain metabolically active but no longer proliferate unless called on to do so depending on the requirement of the organism.
G1 phase is the first growth phase on post mitotic gap phase that lasts between the and of mitotic cycle andinitiation of DNA replication.
G2 phase is the second growth phase or premitotic gap phase in which cell prepares itself to eates cell division, i.e., mitosis.
S-phase is the synthetic phase in which chromosomes replicate, ie., DNA replication, formation of new chromatin fibres, etc.