Q.

Assertion: The points (k-1, k+2), (k, k+1) and (k+1, k) are collinear for any value of k.

Reason: Three points A, B, C are collinear if slope of AB is equal to slope of BC.

1 Both assertion and reason are true and reason is the correct explanation of assertion.  
2 Both assertion and reason are true but reason is not the correct explanation of assertion.  
3 Assertion is true but reason is false.  
4 Assertion is false but reason is true.  

Ans.

(1)

Slope of line passing through (k-1, k+2) and (k, k+1) is m1=k+1-k-2k-k+1=-1     (independent of k)

Slope of line passing through (k, k+1) and (k+1, k) is m2=k-k-1k+1-k=-1  (independent of k)

∵  m1=m2

∴  Points (k-1, k+2), (k, k+1) and (k+1, k) are collinear, for any value of k.