Sodium chloride (table salt,) whose formula is nacl: ionic covalent

Ionic

Explanation:

Ionic bonds are formed by transfer of electrons between metal and non metals.  Covalent bonds are formed by sharing of electrons between non metals

In Sodium chloride

Electronic configuration of sodium:

Sodium atom will loose one electron to gain noble gas configuration and form sodium cation with +1 charge.

Electronic configuration of chlorine:

Chlorine atom will gain one electron to gain noble gas configuration and form chloride ion with -1 charge.

In sodium chloride the one electron from sodium metal gets transferred to chlorine atom and thus is ionic.

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol