Thus, NO₂ is brown in color and acidic in nature, making option (C) the correct answer.
NO₂ (Nitrogen dioxide) is a brown gas and it is acidic in nature because it dissolves in water to form nitric acid (HNO₃) and nitrous acid (HNO₂).

Match the following:
In the following, \( [x] \) denotes the greatest integer less than or equal to \( x \). 
Choose the correct answer from the options given below:
For x < 0:
f(x) = ex + ax
For x ≥ 0:
f(x) = b(x - 1)2