→p⋅→q=0⇒a+b+c=0
a=b=c=0,→ number of vectors =1
For unordered pair (−1,0,1)→ number of vectors =6
For unordered pair (−2,0,2)→ number of vectors =6
For unordered pair (−2,1,1)→ number of vectors =3
For unordered pair (−1,−1,2)→ number of vectors =3
Hence, total number of vectors =1+6+6+3+3=19