Question

question 20 (1 point)
the chemical formula for butyne would be
c₄h₈
c₄h₆
c₄h₄
c₄h₁₀
question 21 (1 point)
which of the following molecules can exhibit cis - trans iso-
1 - butene
2 - butene
1,1 - dichloroethene

Explanation:

Step1: Recall alkyne formula

Alkynes have the general formula $C_nH_{2n - 2}$. For butyne, $n = 4$.

Step2: Calculate the number of hydrogen atoms

Substitute $n = 4$ into $2n-2$. So, $2\times4 - 2=6$. The formula for butyne is $C_4H_6$.

Step3: Recall cis - trans isomerism condition

Cis - trans isomerism occurs in alkenes where each carbon of the double - bond has two different groups attached.

Step4: Analyze each option for cis - trans isomerism

• 1 - butene has a double - bond where one of the carbons of the double - bond has two hydrogens, so no cis - trans isomerism.
• 2 - butene has a double - bond with each carbon of the double - bond having different groups attached, so it can exhibit cis - trans isomerism.
• 1,1 - dichloroethene has a double - bond where one of the carbons of the double - bond has two chlorine atoms, so no cis - trans isomerism.

Answer:

Question 20: B. $C_4H_6$
Question 21: B. 2 - butene