could you help giving me explanation on these problems ? Thank you .

Question 4 Not yet Problem 2. A plant scientist investigated plant uptake of heavy metals (for example, nickel) when four rates of sludge applications were used. For a single variety of sweet corn, a total of 20 plants were established. answer The plants were individually potted and 5 were randomly chosen to receive each rate of sludge. After a designated period of time following the sludge application, the leaves were taken from each plant and Points out of 5.0 analyzed for presence of the heavy metal. The proportion of leaves with the heavy metal was used as the response. What is the experimental unit? O A A set of five plants O B. A plant O C. The leaves Question 5 Regarding Problem 2. What type of experiment was conducted here? Not yet Points out of 10.0 O A Completely randomized design F Fing question O B. Simple comparative design O C. Paired comparison design O D. Latin square design Question 6 Regarding Problem 2. How many degrees of freedom are available for estimating the variance of the error? Not yet Points out of 5.0 P Flag question Q A 13 O B 16 O C. 17 DD. 18