What are the effects of a corporate tax on the WACC of a business?

to reduce tax and to increase equity in case of bankruptcy

I'm not sure what the above is trying to say. Weighted Average Cost of Capital has nothing to do with bankruptcy. It is a financial calculation to determine what the actual costs of funds is to the entity...whether that be funds raised by selling stock (equity...hence dividends or earnings share...made after Corp tax is paid), bank debts (interest is a tax deductible expense to the company, so the rate needs to consider this benefit...at it's own tax rate, and if it even is making taxable income), bonds (which have different rates and tax effects), preferred stock...(yet different)....sale leaseback (depreciation becomes a factor)...etc. Hence, tax is a component or consideration in determining the actual interest cost of funds for each type of the debt (or capital) of a compnay...all types of which are used to determine the WACC.