Answer: The porpoise would hear its echo first because sound travels faster in the water than in air.
Explanation:
The correct answer is b. bimolecular
A cellphone battery is a electrical energy
and a piston in an engine is an thermal energy
Answer: The correct option is 4.
Explanation: All the options will undergo some type of radioactive decay processes. There are 3 decay processes:
1) Alpha decay: It is a decay process in which alpha particle is released which has has a mass number of 4 and a charge of +2.

2) Beta-minus decay: It is a decay in which a beta particle is released. The beta particle released has a mass number of 0 and a charge of (-1).

3) Beta-plus decay: It is a decay process in which a positron is released. The positron released has a mass number of 0 and has a charge of +1.

For the given options:
Option 1: This nuclei will undergo beta-plus decay process to form 

Option 2: This nuclei will undergo beta-minus decay process to form 

Option 3: This nuclei will undergo a beta minus decay process to form 

Option 4: This nuclei will undergo an alpha decay process to form 

Hence, the correct option is 4.
So you would just take the coefficient and put it into ratio form
Answers:
1) 4:5
2)4:6
3)6:4
4)6:6
5)6:4