I’ll try my best to clarify here:
Volatility
Scaling Factor:
=> To convert 1 percent to bps : 100 x 1% = 100 bps. (You cannot change the 1 percent to decimal point, otherwise 1% will not equal to 100 bps). Therefore, the scaling factor is 100
The notional is specified in volatility terms which is $100,000 per vega
\frac{$10,000,000}{100_{bps}} = \frac{$100,000}{1_{bps}}
This means if realized volatility is 1 bps ($100K per vega or volatility point) above the strike at maturity, the payoff will be equal to the Vega notional. (Just look at $10M divided by 100bps to find 1bps, which is $100,000)
Next moving on to Variance
Variance
Scaling Factor:
=> As you know the variance is \sigma^2. Therefore, you can set the equation above from the volatility scaling factor
{(100)^2}\times{1\%^2} = {10,000}\times{0.01\%}
Therefore, the scaling factor for the Variance is 10,000. You might ask why this time 1% is converted to the decimal point first, I will show you why:
Let’s say Var = 4% and if you were to convert 4% to Volatility in percentage without changing it to the decimal point first, you will get the wrong Vol. in percentage. Why? \sqrt{4\%} = 2\%. Because of that you have to convert from 4% to 0.04 first then sqrt it and multiply by 100. The ans will be 20% of volatility.
Back to the Variance point,
\frac{$25,000,000}{10,000_{bps}} = \frac{$2,500}{1_{bps}}
You see if realized var is 1 bps ($2,500 per var or var point) above the strike at maturity, the payoff will be equal to the Variance notional.