If P represent total number of lone pairs (non bonding electron pairs) Q represent total number of a-bonds.R represents total number of o-bondsThen calculate the value (P + Q - R) in pentathionic acid.

Structure of pentathionic acid (H2S5O6)Each 'O' atom contains 2 lp e−s Six 'O' atoms, 6 x 2=12  lp e−1 s Each 'S' atom contains 2 l.p electrons.∴Three 'S' atoms, 3 x 2 = 6 lp electronsTotal lp = 12+6=18P=18Total π- bonds - 4Q=4Total σ-bonds =12R =12∴(P+Q+R)=(18+4−12)=10