A mutual life insurance company must possess at the time of incorporation unencumbered surplus in an amount of at least $200,000. The unencumbered surplus may consist only of:
(1) United States currency;
(2) bonds of the United States, this state, or a county or municipality of this state; or
(3) government insured mortgage loans that are authorized by this chapter, with not more than 25 percent of the unencumbered surplus invested in first mortgage real estate loans.