The modern periodic table has groups. (write your answer as a number.)

18 groups

Explanation: First of all group means that we consider from top to bottom or column in a periodic table.

As we know that periodic table is divided into s,p,d and f blocks.

S -block has 2 groups and P- block has 6 groups and d- block had 10 groups. So total 18 groups.

i'm assuming that it's c.) red bank..

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