If eqaul volumes of 0.1 m naoh and 0.1 m hcl arw mixed, the resulting solution will contain a salt and what

It will contain NaCl.  The acid base reaction will look like this: HCl(aq)+NaOH(aq)⇒H₂O(l)+NaCl(aq)

The reaction occurs due to the fact that HCl (being a strong acid) will dissociate into H⁺ and Cl⁻ while NaOH (being a strong base) will dissociate into OH⁻ and Na⁺.  The H⁺ and OH⁻ will react together to form water and the Na⁺ and Cl⁻ will remain in solution as the salt.  (this is sometimes called a neutralization reaction since the HCl and NaOH neutralize each other.)

I hope this helps. Let me know if anything is unclear.

The formula is (nh4)2co3