Questions

‘Unless’ is used to denote the condition i.e. ‘If’...... ‘Not’. So, again the use of negative word ‘not’ is superfluous. So, the phrase, ‘are not very’ needs to be replaced with ‘are very’ to make the sentence grammatically correct. Thus, the correct formation would be, ‘Unless, you are very careful, you will run into debt’.

Here the answer is 98.

The logic in the given puzzle:

2+3 = 8
3+7 = (7+2)x3 = 27
4+5 = (5+3)x4 = 32
5+8 = (8+4)x5 = 60
6+7 = (7+5)x6 = 72

Similarly,

7+8 = (8+6)x7 = 98.

NH3, Ammonia is a neutral compound as the individual oxidation numbers elements that make up the compound NH3 are Nitrogen (N) and Hydrogen (H) sum to zero. 

We do not speak of the oxidation number of a molecule. We can speak of the oxidation numbers of the individual elements that make up the compound.

Here the oxidation number of Nirogen is -3 and that of Hydrogen is +1.

Now, NH3 = 1(-3) + 3(+1) = -3 + 3 = 0.