When aqueous solutions of are mixed, a precipitate forms.
A) NiBr2 and AgNO3
B) NaI and KBr
C) K2SO4 and CrCl3
D) KOH and Ba(NO3)2
E) Li2CO3 and CsI

A) NiBr₂ and AgNO₃  

Explanation:

We can use the solubility rules to decide which reaction gives the precipitate.

The important ones for this problem are:

The possible products from each reaction are

A) Ni(NO₃)₂ and AgBr; B) NaBr and KI; C) KCl and Cr₂(SO₄)₃

D) KNO₃ and Ba(OH)₂; E) LiI and Cs₂CO₃.

A) Ni(NO₃)₂ and AgBr

Ni(NO₃)₂ — soluble (Rule 2)

     AgBr — insoluble (an exception to Rule 3)

When aqueous solutions of NiBr₂ and AgNO₃ are mixed, a precipitate forms.

B) NaBr and KI

NaBr — soluble (Rule 1)

    KI — soluble (Rule 1)

C) KCl and Cr₂(SO₄)₃

        KCl — soluble (Rule 1)

Cr₂(SO₄)₃ — soluble (Rule 4)

D) KNO₃ and Ba(OH)₂

   KNO₃ — soluble (Rule 1)

Ba(OH)₂ — soluble (Rule 5)

E) LiI and Cs₂CO₃

       LiI — soluble (Rule 1)

Cs₂CO₃ — soluble (Rule 1)

in 1783 cavendish was working with his hydrogen gas and found that when he burned it and condensed the vapor it was water. this was very significant since it disproved the greek theory of elements completely since water was not a simple substance but the product of two gases. it was lavoisier who hearing of the experiment gave cavendish's gas the name hydrogen ("water-producer") and added that hydrogen burned by combining with oxygen and that water was a hydrogen-oxygen combination.

explanation: