Which of the following is a double replacement reaction? ca(oh)2 + h2so4 → caso4 + 2h2o ch4 + 2o2 → co2 + 2h2o 8fe + s8 → 8fes zn + h2so4 → znso4 + h2

That would be the first option Ca(OH)2 + H2SO4  → CaSO4 + 2H2O.

The Ca replaces the H2 in H2SO4,  and the  H2 replaces the Ca is Ca(OH)2.

Option (a) is the correct answer.

Explanation:

A chemical reaction in which there occurs exchange of two ions between two different compounds is known as a double replacement reaction.

For example,

Here, ions of is replaced by ions of sulfuric acid and   of sulfuric acid is replaced by ions of .

When two atoms combine together to form a compound then it is known as synthesis reaction.

When a compound reacts with oxygen to give carbondioxide and water then it is known as combustion reaction.

When a metal is treated with an acid to yield hydrogen gas then it is known as single replacement reaction.

Therefore, we can conclude that  is a double replacement reaction.