Hydrogen is usually –1. This is INCORRECT. The oxidation number for H is +1.
Oxygen is usually –2. This is CORRECT.
A pure group 1 element is +1. This is INCORRECT. It does not follow. This will depend on the other elements and the overall charge.
A monatomic ion is 0. This is INCORRECT. Diatomic ion is 0.
Answer:
The correct option is (a).
Explanation:
We need to find the product of given numbers.
First number = 29.5
Second number = 240
Product of two numbers = 29.5 × 240
= 
Zeroes from numerator and denominator get cancelled.
So,

Hence, the correct option is (a).
The answer you are looking for is A. If you need me to show you how I got the answer let me know. :)
Because if the the technique is wrong the scientist is wrong I’m sorry it’s a bad answer :(