The spider is in the class:- <span> Arachnid
</span>
Answer:
A mnemonic code
Explanation:
A mnemonic code is a memory aid so as to memorize or remember something.
It is code that helps to recall the information it represents easily.
For example :
ATM for Any time cash machine
or VIBGYOR to remember the colors in a rainbow.
To specify instructions these are widely used in computer programming and communications system operations.
The bacteria transform nitrogen into useful forms for the plants; the plants provide carbohydrates.
<u>Answer</u>:
The null hypothesis: the mean egg thickness is 0.2 mm 
The alternative hypothesis: the mean egg thickness is less than 0.2 mm 
In statistics, the null hypothesis states that there is no significant difference between the observed value and the mean thickness. The alternative hypothesis states is the opposite and states the scientist's "idea" behind the experiment. Here, it refers to the fact that due to DDT, the egg shell will be thinner compared to the mean value.