Question

Choose the correct answer:​

(c) A hydrocarbon with molecular mass $72$ is​

• A. an alkane​
• B. an alkene​
• C. an alkyne​

Answer 1

The correct option is A an alkane​

Let’s suppose a formula that can be alkane alkene or alkyne is C${}_n$H${}_{2n+X}$

Where n = Natural number ​

X $=2$ for alkane, $0$ for alkene, and $-2$ for alkyne​

Step 1: Mass of general formula CnH2n+x is ​

= n(C) + (2n+x )H​
= n(12) + (2n+x )​
= 12n +2n +x ​
= 14n + x​
It is given that mass $=7$​

Step 2: Equate mass of alkane with given mass ​
n(14) + X =72 ​

Put the maximum value of n so that 14n should be less than 72 ​ So, n=5​
X= 72-14 × 5= 72-70​
X=2​
X is 2 for alkane​