[firedamage]

what type of chemical reaction for sodium carbonate and HCl?is it combustion reaction or decomposition reaction?the chemical equation is Na2CO3+HCl=CO2+H2O+NaCl.

[Arkcon]

Neither really.  It's certanly not combustion.  Do you know any other types of reactions.  Let's see if you can get an "ah-ha" moment -- keep decomposition reaction in the back of your mind, as you review the other types.

[firedamage]

combination reaction,single displacement reaction and decomposition reaction?

[Arkcon]

That's it?  They don't use the term double displacement, anymore?  Humph.  Well, try that one, and then see what you might try to do next.

[firedamage]

i think metathesis reaction(double displacement reaction),single displacement reaction and decomposition reaction also present in this chemical reaction...is that right?

[Arkcon]

Yes, lets see you write them out, for this particular case.

[firedamage]

HCl undergo decomposition to form H+ ion and Cl- ion..
H+ ion undergo combination reaction to combine with oxygen atom.
Cl- ion and undergo single displacement reaction to form NaCl and CO2

[Arkcon]

HCl undergo decomposition to form H+ ion and Cl- ion..
H+ ion undergo combination reaction to combine with oxygen atom.
Cl- ion and undergo single displacement reaction to form NaCl and CO2

Not bad, but not really what I was going for.  Try this, check you book for another reaction of this type -- some elements will be different, but you'll get some of the same products.  That's a little bit of a hint.  I'd expect the teacher to put that one on the exam, instead of this one.