Natalia began to draw a diagram to compare bases and acids.

which label should be written in the area marked x?

conducts electric current
produces oh– ions
tastes sour
reacts with carbonates

The correct answer is:  [B]:  "produces OH⁻ ions" .

   →  { This is the answer choice that goes in the portion in the circle labeled, "x" ;
 
      → within the "Venn Diagram given [in this very question/problem.]} .

Explanation:


Essentially, the question is asking:  


       "Which of the following answer choices are characteristics of "bases", ONLY ? " ; 

         →   {and NOT TRUE of "acids", only} ; AND:    

         →   {and NOT TRUE of BOTH:  "acids" ; AND: "bases"}? ; 

The answer choices, as posted, are:

   [A]:  conducts electric current ; 
   [B]:  produces OH⁻ ions .
   [C]:  tastes sour ; 
   [D]:  reacts with carbonates.

   →  The correct answer is:  [B]:  "produces OH⁻ ions" . 

   Note that "bases" (NOT  "acids") produce "hydroxide ions"                   {i.e. "OH⁻ " ions} when dissolved in water; whereas "acids" (NOT  "bases")  produce "hydrogen ions" {i.e. " H⁺ " ions} when dissolved in water.

Hence, this answer choice:  [B]:  "produces OH– ions" ;

                                                       →  is CORRECT.


Let us consider the other answer choices:

   [A]:  "conducts electric current" ; is INCORRECT.  This characteristic applies to BOTH:  "acids" (of various types) ; AND to "bases" (of various types) — and NOT strictly to "bases" . 

   [C]:  "tastes sour" ; is INCORRECT.  
        This characteristic applies to "acids"— AND NOT to "bases".  
Note that "acids" tend to taste "sour",  whereas as "bases" tend to taste "chalky". 

   [D]:  "reacts with carbonates" ; is INCORRECT.  
      Note that "acids" — NOT "bases" — react with carbonates ["carbonates" are "bases"] — to produce a salt and water— and release "CO₂ (g) " — that is, "carbon dioxide" (in gaseous form).

      →  The correct answer is:

      →  Answer choice:  [B]:  " produces OH⁻ ions " .

Hope this answer—and rudimentary [yet lengthy] — explanation is of help to you.
    Best wishes in your academic pursuits!