How are the following compounds related

The number of optical isomers for the given compound

$\begin{array}{*{20}{c}}
  {C{H_3} - CH - CH - C{H_2} - COOH} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,\,|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ 
  {\,\,OH\,\,\,\,\,\,\,\,Cl\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} 
\end{array}$

A pair of stereoisomers might be classified in various ways. Which of the  following statement are true with respect to pairs of stereoisomers?

$(a)$ They might be configurational isomers  $(b)$ They might be diastereomers
$(c)$ They might be constitutional isomers    $(d)$ They might be tautomers
$(e)$ They might be conformational isomers   $(f)$ They might be enantiomers
$(g)$ They might be positional isomers

Number of optical isomers in the open chain structure of glucose is

$d-$ tartaric acid and $l-$ tartaric acid are

The total number of stereoisomer possible for $2, 3$ -dichloro butane